hmm, hard one.
ds is 18 and dd1 is 15, so i have one either side of yours.
I think some of the things that bother me about this are:
how far is it? And how easy the journey and how familliar? So if the journey is easy for him, does it all the time, no issues, then that is one obstacle out of the way.
record of being daft. Do you expect him to drink? not great at 16 at a distance from home. What are the implications of him losing iphone etc, can it wait until he has saved up to replace? Is he getting better at this, learning, or if it still an issue. (in the end he will have to learn to manage these things, he has 2 years until he goes to uni)
but the biggest red flag is that he has only net these people online so neither you nor he really know anything about them. They could get him into trouble.
How many? Are they allowed under Covid? Surely you are tier 2, so that means no indoor meeting up etc, how many outside and how many households?
I tend to try and allow where possible, I tend to think the worst that can happen is he ends up staying out too late, misses train etc, and that at 16 he will learn from that.