That's the good news. The bad news is that too many of these turned-on elders are also contracting sexually transmitted diseases such as HIV, chlamydia and genital herpes.
The National Survey of Sexual Health and Behavior, based at the University of Indiana where Dr. Alfred Kinsey led the first large-scale studies of human sexual behavior more than 60 years ago, broke new ground by including the entire age spectrum in its research. It found that many retirees -- especially men -- remain sexually active into their 70s.
Among women 60 to 69 years of age, for example, 30 percent had vaginal intercourse in the previous month; for men of the same age, the figure was 39 percent. Between ages 70 and 79, the gender difference widens: 12 percent for women versus 28 percent for men.
That gender divide is reflected in an earlier University of Chicago study. Thirty-five percent of women 65 to 74 years of age agreed with the statement that sex was "not at all important" in their lives, compared with only 14 percent of the men. For those 75 to 85, 52 percent of the women and 30 percent of the men agreed with the statement.
Experts offer a variety of explanations for these discrepancies. Because women have a longer life expectancy, there aren't enough available men to go around. Many single older men prefer to date younger women. But there is general agreement that, more than any other factor, Viagra and other sex-enhancement drugs have drastically altered the playing field, adding years to older men's active sex lives.
At the same time, most of these reinvigorated elders are failing to protect themselves from exposure to HIV and other STDs. The Indiana study found that only 17 percent of men 60 to 69 years of age had used a condom during their most recent instance of vaginal intercourse with a "casual partner."
And according to a recent report from Massachusetts General Hospital, they are paying the piper. The rate of STDs among men 60 and older taking erectile dysfunction (ED) medications, the report said, was twice that of their non-medicated counterparts.
The connection was strongest with HIV, says Dr. Anupam Jena, one of the researchers, in part because its harsh symptoms are more likely to lead to a doctor's visit than such diseases as genital herpes or chlamydia. That fact has also made HIV the best-tracked STD.
It is often suggested that the incidence of HIV and the other STDs has greatly increased in the past decade, but statistics from the Centers for Disease Control and Prevention say otherwise. For the population as a whole, the number of new STD cases reported each year during that period has been stable -- and that goes for the elderly as well.
Of course, that doesn't include the thousands of infected elders who have few or no symptoms in the short term. They typically go undiagnosed. They may suffer long-term neurological side effects, which can easily be misdiagnosed as standard diseases of aging.
Why don't older people who are single or philandering protect themselves from STDs?
Experts offer some answers: Because the elders grew up in an era when the main reason for using a condom was to avoid pregnancy and that's no longer an issue. Because they don't realize how widespread genital disease has become. Because the men prefer not to wear a condom and the women don't want to displease them -- a function of the male-dominated relationships of their youth and the current disproportionate number of women.
Aside from their avoidance of condoms, the sexually active elderly are especially vulnerable to STDs. Their immune systems' ability to fight off infection has weakened with age. And physical changes in women's genital area leaves them at greater risk for small tears that can lead to STD infection.
The prescription-driven sexual revolution among the elderly has broadened the horizons of millions of men and women, and it has not gone unnoticed by the manufacturers of sexual products.
Last week, the makers of Trojan condoms announced that their line of vibrators was going to move beyond the shelves of sex shops to be sold in grocery and drug stores. For older Americans, said Stephanie Berez, a Trojan product manager, the marketing expansion will provide "a more comfortable buying experience so they can have a healthy and fulfilling sex life."