The practical answer is, you ask them. If they tell you that it's none of your business, then it's none of your business.
Quel-age tu?
no
Only after the fact.
If they abuse a kid.
NO!
Nope.
Check for a pulse - and/or breathing !
Their actions and reactions to outside stimuli.
For example, if you want to say, "they are 14 years old" you would say ils sont 14 ans. :D
They can tell you a convicted felon that is not related to you cannot live with you.
You can usually tell how old a boy is by just guesting his age. You can use math to find out someones age. If you know the person birthday just do the math. Like let say if someones birthday was in 1994 subtract that from this year and you would get eighteen. Some people like that math is not useful but, it really is useful. Well, ask these questions is he my age? Is he my type? Does he like me? Sorry if this did not help you I'm really tried. Well, I hope this helped you.
you wants us to tell you? it was a music festival held in someones backyard