we too have a son, aged 19years, who is currenty in uni and devotes his time to his studies and sport, martial arts, football, cricket, weight training.
He watches his diet not like his dad lol, and rarely drinks alcohol(again not like his dad lol)
We have asked him about girlfriends and his attitude is now and again, and plenty of time for regular girlfriends when he gets his degree.
Seems to have it all worked out, so good luck to him!