I definately think that middle school is too young; Which to me seems like is the time us girls start caking it on.
In middle school, I'd focus on keeping skin clear: Not overdoing it.
I'd say that freshman in highschool could start wearing makeup.
I'm a Junior, and I started in eighth, but I wish I would have waited. It would ahve saved me from skin issues.
An approximate age? 15 or 16.