About two-thirds of women ages 60 and older say they're moderately to very satisfied with their sexual activity, though the level of that activity did decline with age.

Feeling satisfied with one's sex life in old age is closely related to overall quality of life, said study researcher Wesley Thompson, a psychiatrist at the Stein Institute for Research on Aging at the University of California, San Diego School of Medicine.

"What this study tells us is that many older adults retain their ability to enjoy sex well into old age," Thompson said in a statement.

Earlier research has shown that seniors have rewarding sex lives, although men remain sexually active relatively longer than women. That's largely because women outlive their male partners, meaning they don't have someone to be sexually active with anymore, according to a 2010 study published in the British Medical Journal.

The new study surveyed 1,235 women who enrolled in an ongoing research program called the Women's Health Initiative study. The goal of the project is to study causes of death and quality of life in post-menopausal women.

As expected, rates of sexual activity fell with age, as did sexual functioning. As they got older, more women reported problems climaxing and difficulties with arousal and desire.

Of the partnered or married women, 70 percent of 60- to 69-year-olds reported sexual activity in the last six months. For 70- to 79-year-olds and 80- to 89-year-olds, that number was 57 percent and 31 percent, respectively.

However, the women generally did not report regret over the sexual drop-off. About 67 percent of 60- to 69-year-olds said they were moderately to very satisfied with their sex lives. In the 70- to 79-year-old group, 60 percent were satisfied. Among 80 to 89-year-olds, 61 percent were satisfied. [Read: Why Women Shrug Off Lousy Sex]

The differences between groups were so small that they were not statistically significant, the researchers found, meaning the differences could easily have arisen due to chance rather than age. That was a surprise, Thompson said.

"Although the levels of sexual activity and functioning did vary significantly depending on the woman's age, their perceived quality of life, successful aging and sexual satisfaction remained positive."

The researchers published their results online in August in the Journal of the American Geriatric Society.