It turns out Generation Hookup may not be hooking up as much as people thought. According to a new study, the portion of sexually inactive young adults has more than doubled over the past 30 years. Fifteen percent of today’s 20- to 24-year-olds have not had sex since age 18, compared to 6 percent of people born in the late 1960s when they were the same age.

The change was most dramatic among young women, whose rate of sexual inactivity tripled, from 5 to 16 percent; for young men it nearly doubled, from 8 to 14 percent, according to the study, published today in the journal Archives of Sexual Behavior.

It was also more pronounced among people who had attended college, according to part of the analysis which did not appear in the report but which was provided by the lead author. For 20- to 24-year-olds whose education stopped with high school, 6% of those born in the late 1960s had no sexual partners as adults, compared to 10% of those born in the early 1990s. Among those with at least some college education, 6% of those born in the late 1960s had no sexual partners as adults, compared to 19% of those born in the early 1990s.

It may be that this generation is getting a slower start all around, said Jean Twenge, the study’s lead author, who wrote Generation Me, a book about millennials.

“For a long time we’ve known that young adults are taking longer to get married, have kids, buy houses, have a stable job – all those so-called adult milestones are happening later,” she said. “Being 20 to 24 is not what it used to be - it used to be that a lot of them, especially women, were married at that time, or were living with someone and were living independently of their parents. 20-year-olds are like what 16-year-olds used to be.”

Today, more young people live with their parents than in any other configuration, including with a romantic partner.

Millennials are not the only drivers of the change, according to a related analysis of all adults, detailed in the report. Sexual inactivity among adults born throughout the 20th century had been steadily declining, up to and including those born in the 1960s. But then the trend reversed. People born between 1970 and 1979 were nearly twice as likely to be sexually inactive in their early twenties as those born in the late 1960s – a change that may be related to the onset of the HIV crisis in the 1980s. “People born in the 1970s were the first to come of age during AIDS,” Twenge said.

However, fear of AIDS does not seem to be driving the current trend, the study said: among college students, that fear peaked in the 1990s, and does not explain the 3 percent increase in sexual inactivity between young adults born in the 1980s and those born in the 1990s.

So is this the beginning of the end for sex?

“I don’t think so,” Twenge said. “We’ve still got 85 percent who’ve had sex. But there is a probability that we’re looking at a small subset of the population that ends up being asexual, that as society is becoming more accepting of different choices, it’s more okay to say, ‘I’m just not a sexual person.’”