You can lead a horse to water....

Have to agree that willful people don't take advice. In fact, from my experience, they usually end up going in the opposite direction.

I know you said you weren't asking for advice, but perhaps it would be an interesting experiment to refrain from giving him advice and see what happens. Some people make a habit out of depending on advice they can ignore from someone close to them. It's a weird way they function in order to not take responsibility. My H does this-- if I'm talking about a problem he has, in his mind that gives me ownership of his problem and let's him off the hook to a great extent. It's counterintuitive and doesn't actually make rational sense, but it is a thing with some people.

You love your son, no doubt about it. He'll get where he's going eventually, as frustrating as it is at times.