Technically most snakes are sexually mature at a young age (around 1-2 years) but most should not be bred just because they are sexually mature. Even if a snake is able to produce, it may not be safe because it is not of a good breeding size or weight.
It's kinda like referring to the youngest human mother was 5 years old, and most girls mature at 12-14 years old, but it's not the best idea for a 12 year old to have a child.

:]