Yes, this is normal. We've gone through it now with two kids. I think it is preparation for the actual separation, as others have said. As long as he is making responsible decisions and still somewhat willing to communicate with you on the big stuff, it's all good.

He may have some romantic activity going on. That tends to make a teen clam up. And it would be perfectly normal for them to be private.

Yes, totally normal. That's what kids do - they separate before they separate! It's for your benefit. He may start to pick fights with you too.

DS is going to college in the fall and it seems like our relationship has changed pretty radically. This isn't a bad thing but I am wondering whats typical. He's much more independent, much less likely to share information about his day, what he does at school, etc. He's spending much more time with his friends. It feels like he's separating in advance of separating. His grades haven't dropped and I don't see him engaging in risky behaviors. He's happy. Its all good. Just feels weird. Is this normal?