tbh that's a trope that actually makes a ton of sense to me because it explains just how and why they're qualified to be heroes/superheroes in the first place. It makes it easier to suspend disbelief if we're told that this teenager who has incredibly mature judgment and physical abilities has actually been fighting on battlefields since they were a little kid because at least then it makes some modicum of sense and there's an in-universe explanation for why they're capable of things that ordinary teenagers aren't.