Hey roasted, fish and kozi.
Im 15. It sounds like I have the same thing as you guys. Ive also noticed that many guys have a chest dent to some extent. It seems alomost no males I know have a completely flat chest. Our dent may just be a tad deeper.
I did research on this "pectus excavatum" and it looks like we have absolutly nothing to worry about. People with this problem, their dents are huge. You could easily fit your entire fist in one.
However, one problem remains: its kinda ugly.
Thats all we have to worry about, and if it bothers you enough, there is a surgey to corret it. But thats up to you to decide if you want to go that far with it.
Good luck