I have a forty gallon tank full of them. The two largest breeders are now 5 years old and about 9 inches long. They have a small school of 11 of their offspring.

Funny story really, I keep them out of respect. The two breeders are the survivors of a feeding frenzy! They were both about an inch long (from now deceased breeders I had) and somehow managed to escape half a dozen axolotls. After I waited a few weeks and they grew to large for my axies to eat. So they got their own tank. A year later they bred on their own without any special care. I was impressed enough with them that they and their kids now have the job of aging water for use in my other tanks.
My goal is to build them their own pond in the future.