The first task for Prince William on his New Zealand visit is in essence another coming of age for the young royal, second in line to the British throne.

On Monday William opens the Supreme Court as the Queen's representative - the first time he has represented his grandmother in an official capacity.

During his stay he will squeeze in a look at the Eden Park upgrade, sail a yacht on the Waitemata, tour Kapiti Island and get to chew the fat with Prime Minister John Key at a barbecue.

Then it's off to Australia for a series of less formal engagements.

They include a visit to an inner-city community centre in a depressed part of Sydney, after undergoing a traditional Aboriginal welcome, and then a round of live-firing practise with 3rd Battalion, The Royal Australian Regiment.

Duty, charity and the forces.

The three will always play their parts in his life, as they do in the lives of all male royals: but it is going to be up to him to settle, very soon, the precise mix of the three which will, in so many ways, define him for the next few years, perhaps decades.

Even Charles, his father, a man oddly estranged from self-criticism despite all the introspection, is said to accept that his own vacillations during his twenties - was he to be a political royal, a playboy royal, an environmental royal or simply king-in-waiting? - prevented him from defining any fulfilling role for himself: some would say the damning vagueness of ill-definition still haunts him, almost 40 years on.

No one in "the firm" remotely wants the same ethereal miasma to smother William Arthur Philip Louis Mountbatten-Windsor, who could be facing a long, long wait himself before he becomes William V.

Despite the interminable speculative ramblings about the crown "jumping" a generation, the Queen (with memories of the Edward VIII fiasco) loathes the idea of abdication, and the idea of Charles willingly passing up kingship is unlikely.

So, at stake this coming year is the future happiness of a personable enough young man. And quite possibly, the future happiness of the monarchy.

Why this year? Partly age, of course. William will be 28 in June, only eight years short, incidentally, of the age his mother was when she died; it's getting late in the day to be making a career choice, even for a "career" which you could argue has to be thought about more than most. He may, also, be getting married, which can tend to focus a chap's thoughts about life. Certainly, speculation over an imminent engagement is hardly new.

Few things age as fast as cultural references, and the fact that most of the last batch of stories about forthcoming nuptials to Kate Middleton included references to "commemorative mugs and tea-towels from Woolworths" says much.

But it looks this year, with the couple back together and the earlier "split" now seen as half-hearted at best, almost done to confuse and exercise the hysterical, hated media (yes, they all still hate us) as if "Waity Katey's" time might have come.

Hosts of modern couples in their twenties now split and reform two, three times before marriage.

Even the more vicious bits of gutter-sniping about class and "suitability" - that woeful sneering about her mother's being an air stewardess (forgetting that her father was a pilot) and the like - has, by and large, abated. There is also timely relevance to the fact that this all-important visit takes place Downunder.

New Zealand is still toying, when it bothers to think about it, with republicanism, but it's not that hot an issue. There's more active campaigning in Australia, 10 years after the failed referendum on the issue, but even hardline anti-monarchists exude a sense of fatalistic resignation.

Speaking about what might happen on the Queen's death, even the head of the Australian Republican Movement, retired major-general Mike Keating, said: "Perversely, if Charles and Camilla take over, the old Aussie ethos will say: 'He's in there now, and maybe he won't be such a big dolt now that he's the monarch. It's only a fair thing to give the man a go'. "

And William's visit won't hurt.

Charles and, in particular, Camilla, are still broadly unpopular - as they are in other overseas territories; witness the recent lukewarm receptions in Canada - but William is still linked to Diana, who was wildly popular, even among confused republicans.

So he's going to be doing his bit for the family, increasingly so. The recent surprise announcement that he's signed on for a further five years with the RAF means he can't throw himself into that kind of work fully, but the gates have now been opened; we will be seeing more of William in public.

What kind of William will we be getting? In truth, they would seem not to have done too bad a job. In a world of unparallelled media scrutiny - even the actual heir, Charles, still had it easier in his twenties - the decision to send him to St Andrews, and his decision to stick with the forces, have saved him from the madness of a goldfish-bowl life.

By all accounts William has emerged far more "normal" than may have been expected. The success of the hands-off deal with the media for the university years - the only people to properly intrude were, of course, Ardent Productions, headed by his uncle, the shiftless Edward - meant he was allowed to have friends, get drunk, shop in supermarkets, meet a girl (Kate), even live with her: the trusted if insular Scottish town proved the perfect choice. The forces, too, have allowed a certain equality with other ranks; and, of course, fabulous privacy.

In recent years, as often happens in the twenties, both he and Harry have begun getting on splendidly with their father. They email "Pop" constantly, and gleefully showered him and Camilla (around the corner, away from the cameras) with confetti at their Windsor wedding.

The brothers, who share a rented flat when on service near RAF Shawbury, have also grown up emotionally in increasing spurts over the last four years, and recently jointly opened their own charitable foundation (perhaps aiming to emulate, but jointly, the unarguable success of the Prince's Trust), and have their own dedicated joint private secretary, and their own press officer.

William spent a night in sub-zero temperatures on the streets of London to raise awareness, rather successfully, for Centrepoint, the homeless charity that was one of his mother's favourites. Insiders there say that, apart from being the first royal to go this far, his visits to Centrepoint are genuinely welcome, his conversations with the disenfranchised and dispirited lengthy, and honestly curious.

As with the looks - his mother's big eyes and girly cheeks, his father's thinning pate - he's taken a good whiff of both gene sets; along with the sense of duty, which he can hardly avoid, there's a warmer, more tactile nature, which, if we're going to be stuck with a monarchy, surely bodes better than it might have.

He has also, over the past three years or so, appeared to have lost a certain gaucheness, surely part of the RAF life; there are precious few accounts of late of the blushing and mild stooping.

Not a badly rounded young man, then; and when he decides, soon, whether the main ingredient in his life will be the duty - with all the travel and sights (and boredom, and fawning, and press) - or the security of the forces, or the ability to make quantifiable visible differences to poor people's lives, he will have strong friends and mentors, up to and including his father, to call upon.

And here's a fair old irony. For all Charles Spencer's populist talk at that sad, mad funeral, of "the boys" needing "more than one mentor" in the coming years, meaning not just Charles, it has, actually, been Charles and the family behind every wise decision; and father and son are now immense friends.

The royals ignored Spencer, and the tabloid shrieks, and did, as they always did, their own just-wise-enough thing, to survive; and have produced a viable heir, better than might have been hoped for: a posh-boy with the common touch, and a warm if rather Sloaney sense of humour.

Not that it's been a hard, hard life. There has been, of course, frankly insane privilege. Never mind the money, the travel, the experiences, the pretty girls, the loopily posh showing-off in personal helicopters and the like, the expensive tastelessness of favoured clubs. You just need to remember that, when he did his A-level art history project on da Vinci, he was able to refer to his family's own personal collection: a normal life this has not been. Also, he might one day get to be king, which is nice, surely. And he inherits £9 million (NZ$19.8) million of his own (from Diana) when 30.

Set against that the downsides. Whether he decides to retreat with a certain haughtiness or be glad-handingly and taboo-breakingly "normal", he will face constant sniping and attention for the rest of his life from three of Britain's nastiest groupings: tabloid press, jealous courtiers, and west-London snobs. Is it all, in the end, worth it?

Never mind Charles' dilemma; this is the one which has dogged every single royal since Victoria.