I have a huge smile on my face! I loved reading your question!!
This is my oldest son-- exactly!
He is now 18 yrs. old and going off to college in August and he is not silly.
He is a serious young man. But he is very bright.
In 7th grade he had the reading level of a college freshman. He is very responsible. He got a job as a 15 year old as a lifeguard, despite other kids telling him he'd never get hired as a 15 year old. He got a fabulous evaluation at the end of the season and a nice raise the following summer.
I think it's the way they are wired when they are born. I have not found a way to change it. But I think (I hope!) he relaxes more around his friends at school than he does around adults or on the job. My best suggestion is to encourage tolerance of others with your son. My oldest once went on a youth retreat where their were skits and games, etc...all weekend. He didn't enjoy it that much. He got a lot out of the Bible Study and small group time. And he started to ridicule some of the others who were goofy the whole weekend.
I had to talk to him several times about the fact that everyone is different. Just like he wouldn't want people judging him for not participating in the skits, so he shouldn't judge others b/c they love the skits and don't really want to settle down for Bible Study.
I am kind of that way, too. Guess I understand him. Once I attended a weekend continuing ed. workshop. By Sunday afternoon, we were all tired and ready to leave. The leader of the last session wanted to wake everyone up and "bond" one more time. Turned on some hip-hop music and wanted everyone to free dance for 3 minutes to "make us alive again." It was horrible.
My son is very constant. He is like a rock. Don't know if yours is that way. It takes a bit to make him really excited, but it also takes a lot to really tick him off. He is very predictable---steady---solid. Unlike my other kids. yikes.
Your son will find his own "niche" and the way that he can use his gifts in life. Just offer him lots of opportunities to try things and be exposed to a variety of things without forcing anything upon him. (Like that stupid "free dance" I had to do.)