I had this same problem, my gf at the time had an ex bf that was like 16 while I was 19. He started sendin me emails sayin him and a buddy were gonna kick my as$ in town, parents tried to get me fired from my job, and sue the company I work for, just ignore them, he'll get what's comin to him.
p.s.
now the kids is like 17, his parents blew all their lawsuit money (sued the state prison, not my work) and he has a kid on the way, no career (mows lawns in summer)......people get what's comin to them imo