In the 1980s and 1990s they were told they were going to die young, so they gave up their jobs and cashed in the pensions they wouldn't need, buried their friends and tried to make the most of their last months on Earth.

Decades later, thousands of men and women with HIV in the UK, US and across the world are heading into an old age they never expected to see. In the US in 2001, 17% of people with HIV were over 50. Now that figure stands at 39% and by 2017 it will be half. In the UK, the Health Protection Agency says one in six people (16.8%) being seen for HIV care in 2008 were over 50 – and that will double in the next five years.

Many of those who were saved by the discovery of antiretroviral drugs in the early 1990s felt it was a miracle to be alive. But life for the survivors of HIV, as they age, is bittersweet. Many are poor and have long since been edged out of the workforce. Half a lifetime spent on powerful drugs has taken its toll. Aside from the physical health issues as a result of the virus, there are high rates of mental health problems too.

John Rock, from Sydney, Australia, was diagnosed with HIV 30 years ago. "My partner started getting sick in 1983 and died early in 1996," he said at an international Aids conference in Washington DC. "Many of my colleagues and friends were pushed out of the workforce around the mid-90s because they were not well enough to work. Subsequently triple combinations [of antiretroviral drugs] came along and they are still alive, but at the peak of their earning capacity they were out of the workforce for 10 years. Now they are destined for a retirement they thought they never would have, but it's going to be in poverty."

Lisa Power from the Terrence Higgins Trust (THT), who spoke at the conference about the ageing HIV-positive community in the UK, acknowledged the unfortunate consequences of advice from support groups to those who were thought to be dying. "In the 1980s and 90s we encouraged people to give up work and go on state benefits and not be economically productive," she said. "Now we have condemned people to live on an old-age state pension."

Money is not the only need. Many feel lonely and isolated. In a video made for a project called The Graying of HIV in the US, Bill Rydwels, 77, from Chicago, recalled a time of terror and sadness when Aids was scything down his friends. It was nonetheless a time of warmth and support that he no longer has. "It's just so much better today and yet it is a lonelier time. Years ago it was a time that we all spent together. It was a terrible time and a wonderful time because you got to know everybody very, very well. They cried on your shoulder and laughed with you. You don't get that any more."

Recent research from THT in the UK reveals similar sadness. James, 61, a gay man living in the UK who did not want to give his full name, is suffering from serious health problems, including blindness resulting from the use of an experimental drug to treat another condition (not HIV). "My life is empty," he told researchers. "I have tried so hard over the last 10 years to fill the emptiness. Worked really hard at it. I am in a cul-de-sac. It would be nice just to have somebody to telephone.

"I am fed up with people at the top of HIV organisations saying because there is combination therapy everyone is fine. People with neuropathy, and in wheelchairs, we are the forgotten people."

Half the world away, in Africa, which now bears the brunt of the epidemic, the numbers of older people with HIV are also rising fast. Epidemiologists at the University of Sydney estimate that there are more than 3 million people over 50 with HIV in sub-Saharan Africa, and that the figure is rising rapidly.

Ruth Waryero, from Kenya, now 65, had an HIV test when she was 48. She went home and told her husband. "He listened to me and then he got up and said, it's up to you.

"Take care of yourself – I'm off. Since that time I have not seen him again and yet he was the breadwinner in the family. He left me with the four children and two years later I had two grandchildren.

"In Kenya we have different problems [from those in Europe]. Older men try to get younger women for sex. They ignore you because as far as you are concerned, you are finished. You don't need sex and they can apply to the young girls.

"But when you are old you are likely to be raped by those who are positive because they believe if they rape you, as old as you are, they will turn negative."

Older women also face embarrassment at clinics when they go for tests or drugs, she said. They are asked who they are collecting the drugs for.

"You are not supposed to have sex at your age," she said. "As a woman they ask if you are a sugar mummy. I say this HIV came from an old man and the old man has run away from me."

The older HIV generation – in Africa and elsewhere – is not only made up of those diagnosed years ago. Some are people who have been diagnosed late, having lived for years without knowing they were infected. And many people are now becoming infected later in life.

Laura, who took part in the THT research, is a white, heterosexual, divorced mother of two. At the age of 52 she started a new relationship and then suddenly became ill. Because her symptoms were similar to those of a friend who had been diagnosed with HIV, she took a test. When she was told it was positive, she felt numbness and shock, she said. She cannot believe, as a well-educated person, that she stopped using condoms with her partner and allowed it to happen.

Mark Brennan-Ing, from the Aids Community Research Initiative of America, told the conference of the "fragile social networks among people living with HIV in the US and Europe". Families have abandoned them or do not give them enough help, meaning they end up relying on friends, who often have HIV themselves.

Men who have sex with men, he said, are much less likely to have partners, spouses or children to care for them in their old age. Many of those interviewed live in fear of encountering hostility and rejection in care homes. A 52-year-old gay man from London told the THT: "I am somewhat fearful of a lonely old age. In practical terms, if I become mentally or physically frail, the prospect of being the only gay man in an old people's home is very frightening indeed."