Yes, I agree it's very comforting to find that we are not alone in this.
I am not a doctor, so this is by no means info that you should take without double checking with someone with more credibility... However you might want to wait for a while.
Even if the family history shows a tendency for Gynecomastia development, there is the possibility that it may go away.
What's more however, is that if he is still going through the hormonal chaos that is puberty... It's theoretically possible that his gynecomastia might resurface.
Anyways, good luck with your son.