About 130 people will work for the organisation, which is being launched this week. Age Concern is investing about £5m in it, with up to £15m more expected from commercial partners over the next five years.
There are 20 million people aged over 50 in the UK. In 10 years, this age group will constitute half of the adult population.
Ailsa Ogilvie, director of Heyday, said: "Heyday is a membership organisation to help people prepare for a secure and fulfilling retirement.
"Baby boomers are reinventing retirement. They don't want to settle in front of the fire with their slippers. It's a time for new opportunities."
A Heyday survey showed 59 per cent of people want to work beyond the state pension age, but 64 per cent believe it is impossible to get a new job within 10 years of retirement because employers fail to appreciate their experience.
The charity is launching a survey of up to 11 million people to get their views on retirement, ageism and pensions, and the results will shape Heyday's lobbying. It will operate independently from Age Concern, but is legally part of it.
"People think of Age Concern as a service provider for frail older people," said Gordon Lishman, director general of Age Concern. "We wanted to set up something that was more fun."