This is the EXPERIENCE project. You should be allowed on it at any age 13 and up as long as if you're under the age of 16 you are supervised. It's good for children to be opened to other people's life experiences.
No real right age, just the ability to write comprehensible English!
Personally I think the age of consent, so in UK 16, but how can you enforce that? As long as it is not my children logging on just hope the youngsters who do take care.