Mine is currently about 5" or so. I got him as a picked on 2" at the LFS
and so began my puffer journey. I have seen various potential sizes for them in captivity, anywhere from 12-18". Bizzybeas, how large was yours in 4 years?
Here is a reference picture, although he was a little smaller in this pic:
With his personality, it is a very cool fish. And I had once thought my freshwater oscars demanded attention!