I'm 21 and have been on the pill since I was 15. There are lots of people that go on the pill and are on it for 20 years before they decide to try for a baby.
There's no harm in being on the pill long term. It just might take a little longer to concieve when you come off the pill then for someone that hasn't or it might take no time at all. It all depends on when you start ovualting (after coming off it) and how regular you ovulate and how quickly your body adjusts to not having the artificle hormones.
I came off the pill in 2009 for medical reasons, and I fell pregnant within 6 months. So after coming off the pill if you don't get pregnant within 12 months go and see your doctor if you're under 35 6 months if you're over 35.