Like most things in life, if you waited for the right time to do something then it most probably wouldn't get done! I had my first son when I was 29, we had all the necessary components in place, a stable family, a good home and the ability to support ourselves financially. The time spent prior to having our son was enjoyed to the full, with nights to ourselves, impromptu weekends away, regular sleep-ins and spare cash! My wife and I believed we should have time together to develop our marriage before starting a family! Mid to late twenties is an ideal time to start having children as in reality there is most often never a right time or a right age. If you have children in your teens then you miss out on the best parts of being a young adult, that being said, when they are grown up you will still be young enough to hit the town for a night on the tiles!
My answer to this question is 24-29 years old.