Believing in common stereotypes about ageing can trigger depression and anxiety in older people, a psychologist warns.

Older people risk depression and anxiety if they fall into the trap of believing stereotypes about ageing, a psychologist warns.

Bob Knight, a professor of psychology at the University of Southern Queensland, says many older people fall into the trap of "introjected ageism" and mistakenly blame many of their problems on age and believe there is nothing they can do.

"We confuse illness and disabilities that are roughly associated with old age but we think of them as always associated with old age," he told AAP.

"There's a belief that any changes in our abilities means everything is starting to change - it just isn't true.

"If your hearing is bad it doesn't mean you will also have trouble walking or trouble with your eyesight."

Issues around ageing are becoming more important as Australians are living longer than ever before, with nearly half a million people aged over 85 and that figure expected to more than double in the next two decades.

An Australian Human Rights Commission report about the stereotypes of older Australians in 2013 listed some of the most common ones as being forgetful, lonely and isolated, as well as likely to be sick.

Prof Knight says when older people believe such stereotypes they are buying into "introjected ageism", which changes what they think they can do and can spark depression and anxiety.

"A lot of people assume depression is normal later in life and there's nothing you can do about it. Neither of those things are true," he said.

Living in retirement villages or neighbourhoods dominated by older people can also pose particular challenges because of the number of ill and dying.

"There's a lot of people with severe cognitive impairment around. It can create an image that that's a normal part of ageing and it's also going to happen to you rather than an illness that happens to a significant number but not the majority of older adults," said Prof Knight ahead of an address to the Australian Psychological Society Congress in Melbourne on Thursday.

His advice for overcoming ageing stereotypes is for older people to think about the realistic likelihood of illness and dementia.

He recommends older people indulge in the things they have always enjoyed and try ones they may have put off because of work and child rearing.

But one of his biggest tips is for younger people - put more thought into what you want to do in retirement.

"We spend tonnes of time preparing for our work life but almost no time really preparing for post retirement life," he said.

"I think one of the things that is usual about stereotypes and biases about ageing is that you do wake up one day and find yourself as part of the group that you have those stereotypes and biases about."