Most females must be burmated twice before reaching mating size, male only once.
But its a question of growth. When garters are captive breed for some generations it possible that they can breed after only 9,5 month.
Then they need to redouble their wieght about seven times.
That means in average 6 weeks for 1, 2, 4, 8, 16, 32 and 64 gramms.