A bit over an hour, with two changes, back by midnight. Is he going to be pushing the last tram/train/bus? Is there a fallback if he is, and misses it? (Nightbus, known reliable cab number, Uber account?)
Seems OK to me - but bear in mind I don't have any kids, and think it was entirely reasonable of my parents to let me go to Poland by train when I was 15, shortly before the Berlin Wall came down. I'd been doing 10 miles home from school - a walk through Edinburgh, then a bus - on my own since I was 8.