How fast can puffers grow?

[T Kim]

Hi! I have read quite a bit of the info on this site and it is really great! I am curious though, just how fast will the lined burrfish grow? Also, I was sent 2 of these fish, each about and inch and a half long. They are doing great together now in a 50 gallon tank, but can they actually stay together long term? I have found a lot of mixed answers on line, and am curious as to what you all think. By the way, I do have a 125 set up that I can move them into when they get bigger.... Thanks! T Kim