Absolutely not!
I was diagnosed with diabetes at 14 and went through the whole process you'd expect anyone to go through from 18-22. I went to university and probably spent five out of seven nights a week 'out'.
Granted, 'going out' will require a little more forethought and the best advice I can give is for him to literally practice drinking in a reasonably safe environment (ie. party at home maybe) so he can learn how alcohol affects him, so he can start making plans around it. He will have less than perfect control but that's the trade-off that needs to be made.
More immediately practically, I've never had an issue getting into clubs with insulin on me (most doorstaff are trained to be aware of this) and hypo kit hardly needs to be extensive - a pack of glucose tablets in a pocket should do the trick. Plus, clubs also have an unlimited supply of hypo treatments in the form of the soft drink tap. I've been in plenty of clubs where I've been aware I need to take some action to stop a hypo and hey presto, a glass of regular Coke not only solves the problem straight away but also doesn't draw any attention as it just looks like you're drinking a spirit and mixer.
As for your other situations....actually, he can dive. I should know, as I used to be a BSAC Club Diver (I might possibly still be one technically but I haven't been for a few years) - BSAC do pass medicals for people with diabetes, and although the process is more involved than the standard diver medical, if you can show you're in control, you can still pass. You can even still be a pilot - the UK is actually one of the aviation jurisdictions where even people with T1 can fly commercial aircraft (provided they pass the relevant medical requirements).
If you want to give him a bit of confidence, I don't want to come across too much like I'm blowing my own trumpet, but since I was diagnosed, I have:
- Passed my driving test
- Dived the Great Barrier Reef
- Climbed mountains in Asia
- Lived in the Middle East for a couple of years
- Flown a glider
- Done a parachute jump
- Graduated from university
- Driven a canal boat
This is in addition to all the usual stuff you'd expect people in their teens and twenties. And I'm also pleased to say, I'll be getting married this summer too. I know your 19-year-old won't even be thinking about that sort of thing, but the point is, as long as you've got your insulin, glucose tabs and tester with you, there is literally NOTHING you cannot do if you're prepared to put the work in. The world is at his feet and he is in complete control of his own destiny.