From Rosenthal et al. (2001)
 

     % indicating various reasons for first intercourse

                     Age of First Intercourse

                    <15       15-16         17+

Reason

"Made me feel        18%        11%         10%
grown up"
 

"My friends were     39%        19%          0%
All doing it"
 

"I was in love"      18%        35%          65%