Researchers say the age at which a person first has sex may be linked to how well they age later in life.
US survey data have long suggested that first sexual intercourse commonly happens in the late teenage years, with 17 often cited as a typical age in older national estimates. More recent CDC data also show that most Americans have had sex by age 20, although the exact figures vary depending on how sex is defined and which age group is being measured.
That wider context matters because scientists are increasingly studying whether the timing of early-life experiences can be connected to health decades later.
A study led by researchers at Shandong University in China now suggests that the timing of a person’s first sexual experience could be associated with outcomes seen in the aging process.
Rather than tracking one group of people from adolescence into old age, the team used a method called Mendelian randomization, which looks at genetic variants linked to a trait and tests whether that trait appears to have a likely causal relationship with later outcomes. In this case, the researchers examined large genome-wide association datasets on age at first sexual intercourse and several measures of aging.
The paper, titled Evidence for the causal relationship between age at first sexual intercourse and multidimensional aging phenotypes from a full life cycle perspective: A mendelian randomization study, assessed six aging-related outcomes, including longevity, parental lifespan, self-rated health, healthspan and the frailty index.
As part of the research, scientists examined genetic databases to identify DNA markers connected to the age at which people made their ‘sexual debut’. The analysis drew on summary-level genetic data from large European-ancestry cohorts, including UK Biobank-linked studies, rather than direct clinical records from about 400,000 people being newly assessed in this project.
The team reported that genetically predicted later age at first sex was linked to more favorable results on several broad aging measures. In contrast, genetically predicted earlier sexual initiation was associated with poorer overall aging profiles, shorter longevity-related outcomes and higher frailty.
Kaixian Wang, lead author of the study, said:
“Frailty index, miserableness, chronic obstructive pulmonary disease (COPD) and attention-deficit/hyperactivity disorder (ADHD) appeared to play especially important roles.
“Our findings suggest that the timing of first sexual intercourse may be connected to aging through multiple psychological, behavioral, and disease-related pathways.
The expert continued:
“Nonetheless, our findings do not mean a single behavior determines a person’s future health.
“Instead, they highlight how early-life experiences may cluster with mental health challenges, chronic disease risks, and functional decline over time.”
The researchers said frailty appeared to be the strongest mediator in their analysis, while emotional distress, COPD and ADHD also explained a meaningful share of the apparent link. In other words, the study suggests the relationship may reflect a chain of related risks across the life course rather than one simple cause-and-effect pathway.
The researchers said the findings underline the importance of identifying and addressing health issues as early as possible in order to reduce the risk of problems later in life.
Long Sun, who also worked on the study, added:
“Prevention and intervention across the life course may help reduce later health disadvantages and promote healthier aging.
“Our findings further affirm the value of early sexual health education and broader support for adolescents who may be at higher risk.”
Although the team found a connection between age of first sex and aging outcomes, they are still uncertain about exactly why that relationship exists.
They believe several possible explanations could be involved.
They have suggested:
“This may be attributed to elevated risks of unintended pregnancies, sexually transmitted diseases, substance abuse, and physical health conditions during adolescence and adulthood, which are closely linked to earlier sexual intercourse, and can significantly compromise life expectancy and elevate aging-related vulnerabilities.”
The authors also acknowledged important limitations. Their analysis was based mainly on people of European ancestry, meaning the results may not apply equally across all populations. And because the study relies on genetic and statistical inference, it cannot prove that the age someone first has sex directly determines how they will age.
That distinction is crucial: the findings point to association and probable causal pathways at the population level, not a prediction about any one individual’s future. Family background, education, poverty, access to healthcare, mental health, smoking, alcohol use and other social and behavioral factors are all likely to shape the outcomes seen later in life.
Even so, the research adds to a growing body of work suggesting that adolescent experiences can have long-term health consequences, and that earlier support, better sex education and broader preventive care may all play a role in healthier aging.