I don't think that thing looks real old. I'd say 50-50 between 3 and 4.
He's got a big pot belly, but not much more that screams old to me. He does have that typical low scoring 8 point frame.
He gets passed another year on my place, but I wouldn't expect a huge jump next year. Most of my neighbors would smoke him though.
Edit-looking again, I'll say 75% 3 year old.