Pits in particular keep growing well after their 1st year mark. If in a few months he's filled out a bit, then he's probably under the 2 year mark.
The vet said he's certain that he is between 12-15 months. He has filled out QUITE a bit since we got him. He was 40 some odd pounds when we got him in Sept. and a went to the vet a few weeks ago and he was 60lbs. He was also a little thin when we got him. He was found roaming the streets in between the hurricanes and they picked him up. No one claimed him and he didn't have a chip! Whoo hoo for us!!