Hi there - yes, insomnia and anxiety/depression (as you probably know by now) are symptoms. Unfortunate ones too, as most of them are. If he's already up and doing sprints though that's great! Good start for sure. Usually sleep and mood get better enough that life is manageable over the first few weeks/months, so keep at it. Sexual symptoms (sorry to say) are usually the most stubborn and the last to shift. But we're all different and all respond differently!
Seems to be though across many recoveries (on this board and off it) that exercise and diet are totally crucial factors. I was in his position myself in October, now I sleep 6-9 hours/night and my mental sides are just enough manageable for work - and I'm WAY older than your son.
Can he sign up here and talk to us? If not it's no problem. Feel free to PM me but I'll probably say the same thing to you privately as I'd say here. Also, if you can make things more public, someone suffering in the future might read and be helped by your posts and exchanges.
See if you can spend the day getting the protocol down, planning it, and getting yourself the herbs in. Start with 7, I'd probably ensure tribulus, fo-ti and ashwaganda were in there (might be better opinions on mine on a "starting out" herb cycle) and gradually build up.
He'll get through it, that's for sure, but it'll never be as quick as he might want it to be. Also the process of getting through it involves big ups and downs, and periods of feeling better then feeling worse - when you start to hit downswings and upswings don't despair at them, they are in themselves a good sign.
So, next thing to do for you both is get a fast started. I went just about a week myself, water and rest only. After that, juice feast. All that's in the protocol. He'll lose a bit of weight but this pays HUGE dividends in helping the gut to heal, helping the liver expel and deal with the finasteride (at least, that's how I've personally read it.) I mean, a STRICT 7-day fast and then a juice feast on their own MIGHT even fix him! Stranger things have... If not, my most swift and solid improvements came about following my fast.