i totally agree with aghadowey. i think the best thing to do would be to email him again, and explain as kindly as you can that you dont want to drag up the past to much, but if he should ever want to talk to you that you are available.
if this guy is young then it might also be that he is in a difficult position with regards to how his mother will take the news. my own cousin in her 60's now can still not talk to her mother about the man who is her father, in fact she hasnt told her mum that her and me are in contact because of the hurt it may cause her mother.
hopefully one day this guy may get back in contact and want to get to know you, for now i would email him an apology for intruding and let him know you wont force the issue.
good luck