depends on what the term means where you live.
Where I'm from, "dating" was going to a movie, going to a dance, etc.
For that, I think 13 or 14 is reasonable.
however, I currently reside in an area where "dating" means "sexually active."
there are even parents who push their pre-teen kids into it.
and, from what I've seen and heard, it's not anything new.