Firstly, welcome to PC!

Going to a pyschiatrist might well be a very good idea, so well done.

I think you should also talk with him about why he does not wish to take hiw medications, and why you want him to take them, rather than simply trying to force him to take them. It might not end up with him taking them, but he might well be more willing to accept your support. (Though don't be surprised if he finds it hard to talk, I always do when my mum tries to talk to me about this sort of stuff)

17 is not too late. Well, at least, I hope it's not, because I'm 18, and I was first depressed at 14, and I'm only just about to see a psychiatrist.