I did AFS (American Field Service), which is similar to the Rotary Youth Exchange. I had a great experience and would do it again in a heart beat. I did it at the same age as your sosne (I was 16 when I left and turn 17 when over there.
I have not heard of RYE, however, my school (which is a private boarding school) deals with Round Square which is top.
I’d definitely recommend a trip for your son, I was going to take one two years ago (my soph year), but I just couldn’t afford it. Everything I’ve heard from my friends who have been on these types of trips is endless praise. Be careful with Germany though, drinking age and smoking habbits