I would say that all but the sex one are 'when you and the other person is ready.'
For sex, I say leave it until marriage because unwanted pregnancies could be a drag...and a lot of the time people are not emotionally ready for the experience.
Right,,,there's one that doesn't fit. But the rest, you need a partner. Or a pillow.... *Tries to eliminate awkward memories of last years party* *Shivers*
Developmentally in terms both physical and psychological, I don't believe in a firm age, as some develop sooner, and others develop later. I'll throw some numbers in that 'feel' appropriate.
Kiss?
Whenever really. 8? I remember sneaking into a forest with a curious girl at that age.
Make out?
Err.. *cough* 8?
Masturbate? 14 maybe?
Have a boy/girlfriend? Whenever really. 8? =P Unless the title defers some special priveleges like 'oral' that you weren't telling us about.
I am somewhat irked, though, by the rampant paranoia that has various people making ridiculous non-sequiturs, such that even acknowledging that sexual behaviours can possibly be an aspect of prepubescent life (controversial as this statement has been for centuries) immediately casts suspicions that one would only say this if it were somehow "relevant to their interests". Not that I condone/approve of child molestation, but it's now at the point where this sentiment is obstructing the course of truth and justice, not to mention careers and even normal social discourse.
Perhaps if enough people start complaining the sentiments will turn back to something a tad more reasonable.