well i've had oily skin for as long as i can remember & i'm 18 now. i wear makeup pretty much everyday, & the trick that i've been using is actually pretty simple to keep my skin from oiling up throughout the day. after i put my makeup on, i put a little baby powder over my foundation to sorta "set" it. it helps my makeup to stay put & my skin from getting all oily & gross feeling. you don't have to use a bunch of it, & be sure you aren't left with white streaks from not putting it on evenly. it works like a charm for me, & it's healthy for your skin as well.
xoxo