Not a 100% certain he is just polypay and rambouillet since both of those are pretty much exclusively white sheep....Not saying it isn't possible just unlikely. Could be some through backs to the Finn in the polypay I guess.
My rams pretty much hit their mature size between 1.5-2 years old. My Rambouillet ram tops out right about 300 lbs. While my Dorset is right about 200.
Your guys looks small-ish so I would guess he could go anywhere from 120's-180's when fully grown.
Lambs can be difficult to estimate with out getting your hands on them. Especially since he is in a full fleece.
Are you planning on using him for breeding or as a pet. If he is for breeding don't make him overly friendly! A good majority of the time friendly rams become aggressive rams. If he is a pet I would get him castrated. This will also alter his adult size.
Nope he isn't to young. Lamb is technically anything under a year. Right around 9 months is when most people process theirs. I do mine around 12-15 months and they turn out fine as well.