I am 26, I donated on May 10th of this year to my sister who was 23 at the time (she's 24 now). I'd say I was in pretty immediate pain for about 4 weeks, with the first week being the worst. For the following 5 weeks, I had pain that was a lot more mild, but still there. At about the 9 - 10 week mark, I noticed I really had no pain at all (aside from a lingering sensitivity on the right side of my abdomen when it's touched in certain ways, this sensitivity actually even remains today ..? *I'm trying to be patient*).
After about 3 months, I noticed my energy levels were much improved. Now at the 4 month mark, I'd say I feel about 95% better in terms of energy.
My healing process may have taken a little longer than most people though (especially considering my age), but I did develop an infection around my main incision about two weeks following the surgery, and then I developed an allergy to the antibiotic that was given to me (it was quite the roller coaster to be on!).