OT: How to deal with over worriers?

I have a 14 yr old that is worried constantly about what everyone else things of both him and his siblings.  This is causing a lot of anxiety and stress, pent up tension and starting to show in other ways.  He says they embarrass him, he’s worried what others will think of him (because of what he does or what his brothers are doing).

He has started twitching again and we believe it might be a food allergy so we are going to back to a plan that we tried once before.  He is so worried about what others will think if he can’t eat something he did just a week ago now.

Dh and I tried to assure him no one is going to worry about what he eats.  That he should worry about how God sees hiim and his parents not his friends and others we see.  That what his siblings do does not effect him in any way (unless that is he just set an example and then they follow suite).

I’m not sure how or what to read/do with this.  Any suggestions?  Is it an age thing?  A boy thing?