Older Americans remain sexually active into a very late age, but are more likely to throw caution to the wind when it comes to using condoms than teenagers, said the biggest survey in decades on US sexual behavior published Monday.

Most teens don't have sex, but when they do, condom use has become "normative" behavior, researchers from the Center for Sexual Health Promotion at the University of Indiana said in the study published in a special edition of the Journal of Sexual Health.

Teenage boys reported using a condom 79 percent of the time during the last 10 times they had intercourse with a girl, while teen girls reported using a condom 58 percent of the time, the study found.

Michael Reece, director of the Center for Sexual Health Promotion a lead researcher on the study, called teen condom use "a public health success."

And he voiced hopes that they would carry their sexual habits all the way into ripe old age, a time when many Americans still have active sex lives, but are not as sexually responsible as today's teens.

Although Americans remain sexually active "well into old age (80+)", only one in five men and one in four women over the age of 50 uses a condom, according to the study.

"Freed from concerns about contraception by virtue of age, they remain unclear or unaware about the need to continue protecting themselves and their partners from STIs," or sexually transmitted infections, it said.

"We may need to re-educate older people because as their relationships end or their partners die, if they're dating and have multiple partners, there may be no danger of pregnancy, but the STI risk is certainly present," said Reece.

The study gathered data online from more than 5,300 Americans aged 14-94 about their sexual experiences and condom use. It was the first study to look at such a broad age-spread.

It follows a ground-breaking survey published 60 years ago by Dr Alfred Kinsey, also of the University of Indiana; another nationwide study published in 1994, and several smaller studies about Americans' sexual behavior.

Reece hopes a follow-up study will be done before another 20 years have elapsed, but said it all depends on funding. The current study was funded by a condom maker.

In addition to shedding light on Americans' condom use, the study found that Americans have a vast repertoire of sexual behavior, and are inventive in the bedroom.

A total of 41 combinations of behaviors were reported at study participants' most recent "sexual event", as the study likes to call it.

The researchers also found a gender gap in US adults' sex lives to go with the generation gap in condom use.

For instance, significantly more men - 85 percent - believed their partner had an orgasm during their most recent "sexual event" than the 64 percent of women who said they actually did.

Men also said they were more aroused, had greater pleasure during sex, fewer problems with erectile function, and less pain when they were with their usual partner. Women felt more aroused with a non-relationship partner.

As for masturbation, the researchers found that men did it "strikingly more" than women.

But the big news from the study was that masturbation was finally being talked about openly in the United States, former US surgeon general Joycelyn Elders said in a commentary piece published with the study.

"We have finally included masturbation in our national conversation and as a result stopped checking our hands for growing hair," she wrote.

"Now it is time to include sex and sexuality as pleasurable and natural in open frank conversation about the human condition," she said.

"Talk concerning procreation is not enough, because it neither addresses accurately the varied sexuality of Americans nor the broad range of sexual practice," she said.