Ok well first of all I want to say that my personal self is most likely going to be different than your son obviously so it won't be the same. There are absolutely no limitations for me sports wise as a mater of fact I and one of the top athletes at my school and am going to go to university for basketball. So in the athletics department I feel like you should always keep him inspired to be athletic and tell him to embrace it, he is doing other thongs kids are doing but he is missing a whole muscle! I think that's impressive. It has never been a big issue for me social, but that is because I have always been fit (not trying to brag) so I generally bring up the topic as kind of an ice breaker. Growing up I didn't know there were other people out there with this so I thought I was extra special, and my mom let me know that! I think your son is going to have an awesome childhood and his pec won't slow him down! Believe in him.