Older people are often assumed to want amiable companionship in later life rather than passion-fuelled romance.
But a survey of 2,002 older Britons suggests 52% of over-65s feel they do not have enough sex, and nearly a third are happy to have sex on a first date.
It also found one in 10 over-75s have had multiple sexual partners since turning 65.
The charity Independent Age said its survey showed age was "no barrier to having a sex life".
'You should enjoy life'
Dennis Allen, from Somerset, has not let age stand in the way of his and his wife's sex life.
The 84-year-old married Pauline, 85, his fourth wife, in 2004.
He said the pair were on average sexually active twice a week.
"If you're up for it, you should enjoy life," he said.
"You never know when you're going to be past your sell-by date."
Dennis said both he and Pauline, 85, had made sure to exercise and look after themselves, in part so they remained attractive to each other.
He said: "Let's put it frankly, if you were a young lady and you saw your husband was sitting there with a great big beer belly, smoking a fag out of his mouth, what would would you think? Would you fancy him?
"My wife has always looked very attractive. She won't go out of the door unless she looks the part, and she won't let me go out of the door unless I look the part."
The survey also found:
- Just one in six people aged 80 and over said they felt they had enough sex
- The same proportion of over-65s said one of the only reasons they would stop having sex would be a lack of opportunity
- One in four over-65s in a relationship that started in the past 10 years said they had met online
Lucy Harmer, director of services at Independent Age, said a lot of older people were more sexually active than many people might think.
She told the BBC: "The generation that is reaching 65 and older now is the baby boomers. I don't think anyone has ever told them they should be stopping.
"People of that generation have a slightly different approach to sex, maybe, than the 80 to 85-year-olds did."
'Little discussion of sex lives'
The poll also highlighted that about one in 11 over-65s said they did not take any precautions against sexually transmitted infections when they started having sex with a new partner.
The Terrence Higgins Trust said some older people who were newly single or sexually active later in life had little knowledge about preventing STIs.
Debbie Laycock, head of policy and parliamentary affairs at the sexual health charity, said: "There is still very little discussion of the sex lives of older people, with the vast majority of conversations, education and sexual health campaigns focusing on young people.
"This has created the assumption that sexual health and STIs are only issues for the young - and that needs to change."
- Talk to your partner about how you feel and try to see things from their perspective
- Communicate to your partner about what you both want and need sexually
- Have body confidence
- Experiment - for some that might include having a same-sex relationship for the first time
- Practise safe sex, as STIs can still be passed on