I have read what the concerns here are and let me give you a little insite if I may. I'm 37 years old, I've had two children of my own, my eldest is now 18, and I have three wonderful step daughters through my new marriage. My husband and I are now trying to have a baby together and let me tell you it's been a real challenge! I was always very fertile about 10 years ago and having a baby was not an issue what so ever, now it's something that requires work, timing, ovulation tester kits etc...tends to take a bit of the romance and excitement out of it! I was 20 when my first child was born and at the time everyone I knew around me was having a baby too and I always knew from an early age that I wanted lots of children, so I found myself pregnant at 19, fresh out of high school and on finishing a votech course I was taking. I can say with all honesty, while I love my daughter dearly and would never give up the experiences I had in having her, I know now that I would have enjoyed her so much more had I waited until I was a little older. I know many people say this to younger women who talk about wanting to have a baby like your a child yourself and not ready for this. 
 
I know that some women are ready for it earlier than others, or at least they believe they are, I know because I was one of those women. However, I know now that had I been a little older and lived life a little more prior to getting pregnant at that age I would have had more patience, I would have taken the time to slow down and enjoy watching those things that you can only see through the eye of a baby...the discovery of their world and what lies beyond the tips of their fingers, the first steps and crawling and the pride that comes with that on their part. And I certainly would have been able to handle the up all night, the teething with a high fever and changing out the bedding in the crib for the 4th time by 3am! They are wonderful little beings and they can bring so much joy and happiness into your life, but we tend to forget that they require an enormous amount of work and commitment that at that age we are not totally ready for.  
 
Personally....I would not wait until my age as it then becomes more of an issue with health and genetic testing, etc. but I would hold out at least too 25, if you want that baby this badly right now, you will still want it then and you will be that much more prepared for the 18 years that lie ahead.