Looking back at photo’s of myself as a child I can barely see the sunken chest appearance at all, It just looked like a happy go lucky kid with a little bit of a pot belly:P too many mushy pee’s perhaps. but as you start to get older it definitely starts to develop more and will most likely become deeper.
During my teen years it became very obvious that my chest was different from everyone elses , it was made even more obvious as I was very skinny in my teens, and along with flared ribs it made my chest appearance really stand out.
So around my 20’s my chest pretty much came to a stand still , and it has remained in that state for some time. Its probably due to the fact that human bones are more malleable in your younger years and as you age they become stronger and more in place. This is why I guess they recommend surgery at a young age due to how bendy your bones can be.
So still exercising to improve my P.E and wearing my Posture belt every now and then:)