Channel catfish mature sexually according to size. While fish less than a year old don't normally spawn, they certainly can develop mature eggs. But, that's quite rare. Since you have other species of fish, don't worry about catfish reproducing. They spawn last each spring, after all other fish have finished round 1, so there are usually plenty of other young fish to eat succulent little channel kittens.

Teach a man to grow fish...
He can teach to catch fish...