What age do you feel is the minimum age to travel alone on vacation?

Age for with friends, then age for entirely alone.

Thanks

Well, that entirely depends on the individual.
I would tend to say 14 for both questions, in general

15
17

With friends, are the parents of the friend's going along? If no adult supervision, then I would say 16. I say this because when I was 14 I was allowed to go on holiday entirely alone and I had a GREAT time, more fun than a 14 year old should have!

with friends = 12
without = 14

friends 11
alone 14

I would say 16 with friends and 18 alone. I don't know why anyone would even want to travel alone before they are old enough to be allowed all the rights of an adult.