I too was was an instructor that got the students that the more senior instructors knew would be a can of worms. I don't think I can suggest anything that hasn't been said already and to be honest, I really wasn't successful with them. I'll just add that I noticed patterns in many older students, in that they had a very difficult time learning new things. Hell, I'm 30 now and can start to see how that begins.
I had one older student that I later learned had once smoked pot right before his helicopter lesson... not saying that's your situation but do at least entertain the idea, it sounds like this guy is taking his training seriously though. I just mention that because I had suspected something a couple times but was too young and naive to believe that someone would really do that.
If it makes you feel any better, I've been in your situation and I didn't have the balls at 22-23 years old to tell someone my Dad's age that they couldn't hack it. You're doing the right thing by asking for advice. In my situation, they ended up failing their initial PPL checkrides and then it became my problem.