The way people care for themselves in midlife has a major impact on how happy they will be in their old age.
That means not smoking, keeping fit and staying mentally active, says Professor Brian Draper, a speaker at a Perth congress hosted by the The Royal Australian and New Zealand College of Psychiatrists.
It's also important for people to keep engaged with society after retirement, says the University of New South Wales and Prince of Wales hospital psychiatrist.
The biggest risk group for suicide in Australia is men older than 75.
"In older people depression is probably the major predictor of suicide, but quite a few victims have never had depression before. In many cases it is undiagnosed and nobody else knows about it," says Prof Draper.
One of the major risk factors for depression in old people is brain damage from cerebrovascular disease, which is often related to high blood pressure.
Social issues are also important.
It's a good sign when people say they are busier in retirement than when they were working.
"It is problematic when an older person spends their retirement sitting around watching TV all day and not doing much else.
"That's setting themselves up for boredom and unhappiness."
Most people enjoy social activities, but it is okay to be a loner.
"The key is that people enjoy what they are doing. It does not matter if it is a crossword or a puzzle or a game of cards as long as it has mental stimulation attached to it."
Prof Draper says adult children should stay actively involved with their parents and seek help from a GP if they notice signs of depression.
"People think it is normal for older people to get a bit withdrawn and depressed. In fact it is the exact opposite."
Australia needs a more cohesive mental health plan for older people, he says.
"Mental health tends to be a state responsibility and general health for older people is a federal responsibility."