I had my first child at 15, so I know first hand about these things, and am even going through this with my 8 year old son, who is noticing girls.
I think 16 is a good age to start dating, but as far as kissing, I'd tell her something like, you wouldn't recommend it because it can lead to other things & over shadow the relationship, but when its the right time, she will know.
My childhood was pretty jumbled, so I got an early start at this all. Thats good that she is dating younger guys though, My first boyfriend (and now my husband) is 10 years older than me, so that put a great deal of pressure on me. He did not pressure me into anything, I just felt obligated, as I think many girls do that date older men. Dating younger, kinda gives them something to wait for.