I have to agree with the moms who say you can't assess whether he has anxiety or not yourself. You might have a suspicion - and if you do, then it might be worth seeing a therapist for him. We did.
I can just share with you my own experiences - I had one who used to hate the bus, to the point where she felt ill. I had one who found school really hard (not academics, but the whole thought of it - but had friends, had activities, was into sports, etc.). The one thing that did not help either of them was me talking. That's where I got some good advice from this site. I had to just shut up and listen. I didn't have to solve it (couldn't anyways) or fix things.
We learned techniques - they learned some to help them cope, and I learned how to parent kids who have low anxiety. When they had the anxiety it seemed huge to me - but really, it was manageable. Mine didn't have to go on medication. We just acknowledged they have it, we learned how to validate their feelings (without going on and on), and we just moved on. We had to keep going with our day.
So I have one who still will on occasion say "I feel like I'm going to throw up" and I'm like "go to the bathroom if you need to, I'll wait". She never does - it's just part of our day the first day of school, etc.
The other one would worry to the point where he was just negative. So talking about it was terrible. He'd then obsess because it became a topic of conversation. So we acknowledge it - we work around it - but it's just something that he has to deal with. He's learned tools, and talking to someone else about it who got it (therapist) was huge for him. He only went to about 4-5 sessions. At that point the therapist told me he had his tools, book only if he needs it again in the future. So far he hasn't.
I had about 3-4 sessions with the therapist - to help me deal with it with my kids. Huge help. I hadn't had a clue.
Some is definitely maturity. They kind of have to own their anxiety. Know how to communicate when they have it, and I'm just supportive. My husband is really good too. We remain calm and don't get negative/upset ourselves. If I have to take a moment, I do.
So I don't know if your son has anxiety (only a therapist can tell for sure) but that's been my experience.