Did you go straight into being a pro footballer? Or did you have back up plans? Like "if this doesn't work out, I'll be an electrician" or something?
I've never had super lofty goals, but my parents always supported me in what I wanted to do. They never tried to steer me, but they did ask pertinent questions about what I was planning at various points. Probably to hint at bad idea.
I feel like I could have asked them for money/support at any point for any of my projects/ideas/whatevers, and - after making sure I was serious - would have helped out however they could.
I have a very unique career at this point, and I am only in this position because of the eclectic experience I have. And it is completely unrelated to my dreams as a kid or what I studied at university.
Ultimately, he is growing up. He's going to have to make mistakes.
I'd say you have to be prepared to support him as much as you can in his dream of being a pro footballer.
Maybe he won't be a pro footballer, but he might get a satisfying career out of being football-adjacent. Medic, science, coaching.
Or maybe he will try it for 5 years and eventually realise it's not gonna happen, and be an electrician.
Or maybe he will struggle for 2 years, realise he needs to double down, and make the cut a year later.
I had a friend when I was growing up that dreamed of being an RAF pilot. Everything he did was around that.
Due to some unfortunate life circumstances, that dream was ripped away in the space of a week. Completely out of anyone's control, but he could no longer qualify as an RAF pilot.
He was heartbroken. He's now an engineer/mechanic in the RAF and loves tinkering with cars.
He shouldn't find another dream.
But he should be aware that dreams don't always come about. And if this dream doesn't, would he be happy in an adjacent career? Or something else entirely?
Help him research the backup plan.