Since we're talking about an amoral baby making law, the age bracket 16-36 is more realistic. Doesn't change much in terms of population, but also doesn't explain how it will be enforced.
However this is just the beginning. After that, assuming worst case labour practices, you have another 10-15 years of supporting increasingly expensive unproductive citizens before they can even start to pay back the costs on society they incurred by being born. It's a long slow road...
As usual Neal Stephenson was ahead of the game. The plot to duplicate "A Young Lady's Illustrated Primer" is facilitated by Confucians needing educational materials for vast numbers of girls (maybe clones?) being raised on nursery ships.
However this is just the beginning. After that, assuming worst case labour practices, you have another 10-15 years of supporting increasingly expensive unproductive citizens before they can even start to pay back the costs on society they incurred by being born. It's a long slow road...