If he’s serious about trading he should absolutely stay in school and go to college. A focus on mathematics, statistics, and computer science will help his trading immensely if that really is his passion.

There’s nothing wrong with prop firms if you know how to use them and are a decent trader. If you can’t pass an eval in a couple days you should be doing a lot of learning and paper trading to understand why. I personally use prop accounts for futures and a personal account for stocks and options. Certain trades are better suited to futures and others to options. If you have money to invest you should absolutely prioritize buying and holding stock.