How long a virgin? It’s written in your genes: study. Apparently genetic factors explain around 25 percent of the differences in the age when people start to have sex.

A DNA study of more than 380,000 people has uncovered a rather surprising role for human genes: helping to determine the age at which you first have sex.

The genes likely influence such factors as the age at which puberty hits, and whether or not you posses a risk-taking personality.

The average age of sexual maturity for both genders has decreased from about 18 years in 1880, to 12.5 in 1980, according to the study authors.

Scientists have blamed changes in nutrition and the larger physical size of children today, as well as exposure to hormone-disrupting chemicals.

So in the century from 1880, the age of average age of sexual maturity dropped massively from 18 to 12.5 years. That helps explain why 21 was the age for “coming of age,” and many of the age-related laws.