Go for it and try it; Retin A is great stuff! I have literally been using it (with the exception of a couple months here and there) for the past 10 or 11 years. I am 26 now. What concentration are you using and what is your skin type? My dermatologist (been going to the guy all these years!) put me on 0.1%, which I think is the strongest concentration, in cream form for years and years. When I was a teenager, Retin A Micro hadn't come out yet. When it did come out I asked my derm. about it and wanted to try it. He said I could try it but that he thinks he has seen better results with the creams. I ended up using the Micro but going back to the cream. And now that I am 26, I don't mind a cream and basically am just continuing to use it for the anti-wrinkle benefits (though I occassionally breakout...birth control has helped prevent breakouts during that time of the month too.)
Using Retin A also made me a religious sunscreen user. Try to get an spf 30 if you can. Aveeno positively radiant spf 30 is a really great one with avobenzone, and is great for everyday. I just got back from Europe and met girls 19 and 20 years old with wrinkles and I literally don't have a single line on my face. I think Retin A and sunscreen have a lot to do with that!
So start using it....it's great stuff! Just wear spf everyday!
(oh! and i second the using it once sparingly everynight! i also had a nightmarish experience when i tried using it twice a day and misapplied it! less is more...)