My socially immature teen hangs out with much younger friends. How big of a deal is this?

My socially 15 in December and is a high school freshman. He has always been immature socially. He has always had younger friends and his interest always aligned more with kids who were 2 to 5 years younger. He had no real friends until 3rd grade when he started hanging out with boy in kindergarten. They remained friends until we moved. I was hoping that the move may push him out of his comfort zone but we ended up moving right nextdoor to a family with 3 kids. My son was 12 at the time and their boys were 9 and 7. My son became instant friends with both. It has remained this way for the last few years. They have sleepovers, hang out after school, etc.My concern is that the 11 year old even seems to be passing my son in maturity. My son was hanging out with them on Wednesday and came home sad. He told both boys what he was getting for his birthday and the 11 year old said something like, "Aren't those things for little kid?" The 9 year old was super into it though and my son said he ended up playing with him most of the time while the 11 year old texted friends. This is a reoccurring theme lately. The 11 year old has new friends who don't really seem to like my son and I get it. I'm not angry with the 11 year old. He's a really sweet kid but he's moving past the stage of playing with toys and is getting more interested in other things, including girls, sports, and clothes which my son has no interest in. In fact, two of the shirts my son mentioned he was getting for his birthday were deemed as childish by the 11 year. Both are character t-shirts.So this means my almost 15 year old ends up spending a good amount of time with the 9 year old. Should I try to gently discourage this? That seems cruel but I wonder if he needs to start looking for friends his own age. He is involved in band at school but doesn't want to do any other activities where he could meet friends his own age who share the same interest. He says he doesn't like hanging out with his peers because they are always thinking about other things and don't want to play with toys all the time. via /r/Parenting https://ift.tt/34xV3Vi