Aww, I feel very sorry for him - He was me as a child, multiple times. I was always growing out of things later than others. I have such a vivid memory of coming back from a summer holiday, excited to talk to my friends about the thing we were all "into" only to be told by all of them as a group that they were now too old for it, and they didn't like it any more.
Three paths you can help your son go down:
1, Conform. Encourage him to like older things.
2, Rebel. Do what he wants, when he wants it, fuck all of them.
3, Like his stuff, but keep it to himself so he doesn't get teased.
We all want to be number 2, but truth is most children are not that confident, especially as they near their teen years. It takes a huge amount of confidence to walk in the face of popular opinion as a kid. I wasn't, so I went down the third route, and kept doing what I love. I just learned to do it at home, and not mention it at school. Never got teased, kept my interests.. it kind of worked, but I wish I had been confident enough to do number 2.
Maybe you can help your son be that confident.