Its the breeding of the bird more then likely.
We have gotten poor bred turkeys a few years back and at 1 years old they weighed 15lbs live weight toms on 27% feed full time.
It also could be the breeds that he is.
Also could be that he was fed a poor ration like 16% or lower.
To get birds of standard weights you need to be very selective of the breeder you get your birds from. You need to ask alot of questions of the breeder and ask to see the breeding stock and any birds they might have that they hatched out that have some age on them.
It's hard these days to find a reliable heritage turkey breeder that their birds get to the standard weights in the time allowed. But it is starting to get better !!!