I'm 20 & have a 6 week old baby girl and it is the best thing to ever happen to me. I believe that having children young is the way to go (provided you have a caring partner who will be there for you and wants them as much as you do), as by the time they leave home you are still young evough to do everything you want to - travel etc. Look at your grandparents and great grandparents, chances are they had their children around this age - it has only been in the past 30ish years that people have been putting it off till later.
If you feel you are ready - go for it, there will be the people out there that tell you your stupid and have ruined you life etc. DON'T LISTEN TO THEM - they are generally the ones that don't have children themselves so they are in no position to judge you anyway.
All the best.