I said
but wouldn't this situation be a common one as to why some people find it hard to fly at 18ish?
Your experience
isn't a common one. You've worked earlier than many people and have experienced things other people may not have. So in three years of working from 15, you've had certain experiences and I congratulate you on doing well for yourself. But in three years of the more
common person starting working around 17 or 18 yrs old, that brings them to 21 yrs old to acheive more or less of what you have by 18.
But keep in my for example that a 25 yr old may not get the job either, even if they've flown as cabin crew previously! It isn't always an age issue, of course.