Probably the easiest thing would be to vasectimize males at the age of 13 after freezing some of their sperm. Then you could unfreeze it only after they have enough money to support a child up to the age of 18.
Sarah Boxes (1997-06-22). "The Contraception Conundum: It's Not Just Birth Control Anymore". The New York Times. Retrieved on 2008-02-09.
The Contraception Conundrum - It's Not Just Birth Control Anymore - NYTimes.com