Thats a good question and I was wondering the same thing with sw
species in general. I would imagine some species reach there adult size within a short period while others grow over a period of years.
I always get the smallest hardiest looking fish I can find at the LFS
regardless of species unless there may be a compatibility issue with its size. I imagine you can always return a fish that has outgrown its take to most LFS
a receive some sort of store credit. Local public aquariums would probably also accept these fish as a donation.
Its not a fish but I once had a Burmese Python that reached a size I was no longer able to handle after just 17 months. It was 24 inches when I got it. It still may be at the Cincinnati zoo for all I know.