I don’t disagree with the counter argument entirely, but I do think that the almost ‘discount’ (for lack of a better word) you receive by hiring younger people is excessive. And because it’s less than half the price to hire a 15 year old vs 21 year old, that means 2 things end up happening:

Firstly the older you get the less likely you are to be hired for an entry role (which I’m sure you can argue is justified, but if you just never started working until you were 18+, you’re pretty much SOL)

Secondly once you turn 17, or 18, or 19, a lot of people get effectively fired if they aren’t part or full time. Of course, that would be illegal, so what happens is your hours just end up getting cut, or they conveniently “run out of work” for you and stop giving you shifts