Hart's daughter and show secretary Sharron White said more people are bringing out their young horses and as a result class numbers are growing year on year.
"The championships are a real celebration of the young stock being bred in New Zealand," White said.
Hart said he remembers the early days of the champs vividly.
"In the early days people would breed a horse and have it sit in the paddock until it was six or eight years old."
Hart said it is well proven and accepted now that working horses and competing on them at a younger age gives them better habits.
The championships get under way at the showgrounds on Friday, running through the weekend, with age group finals on Sunday.
Faults are accumulative over the rounds, with the 4-year-olds jumping one round a day over two days.
The 5, 6 and 7-year-olds will be competing over all three days.
If scores are tied, there will be a jump-off in each age group on Sunday.
There will also be a luncheon in honour of everyone who has been involved in the champs over the past 25 years.
New Zealand Equestrian official Heather McDonald is designing the courses in ring one and will be assisted by Olympic silver medallist Greg Best.
Steven Nichols is designing in ring two and Lex Peddie will create ring three's course.
It is the first time a third ring has been introduced at the champs.
Hart, who has been breeding top competition horses for 40 years, said he is proud of what the committee has achieved in running this event.
"I just want to see our sport get better and better."
Hart added that the international breeding pool has elevated the sport in New Zealand.
"When I started all the horses were local content but now we have genetics from all over the world.
"The mares are the secret to success – talent is inherited and it will keep coming back if they have an x-factor."
