I think ENTPs tend to show the greatest range of confidence development over time.
Ultimately most will figure themselves out and grow into extraordinarily confident adults, but it can take time. I've sorted through a lot of insecurities myself, and still working on it.
Just...the differences in the way we approach problem-solving in general have so many implications and especially not really understanding Fe at a young age, it's pretty insane at times. I remember consciously wondering to myself all the time why anyone bothered with any of the behaviors I now label to myself as xxFJ. It was just, wow, that shouldn't theoretically make any sense, see? You must be STUPID!
Probably depends on a million factors, but...teenage ENTP males, especially, are notoriously insecure, as I myself can attest to.