I agree with Sabian. The pictures are kind of blurry, so I can't see much detail. A front view of the face and a side/profile shot is what I'd like to see.
Hopefully these pics of my Grandparents cat will be more helpful than the other ones I posted. His two front paws are bigger than his back ones. He is 4 years old.
In the bottom pic of the 2nd set I thought his paws look funny. He appears to be polydactyl meaning he has an extra toe. I read that originally Maine Coons had polydactyl paws and it was bred out however there are some breeders that actually breed for this trait. Your guy could possibly be full blooded but there's really no way to know without papers or a DNA test. If he is I would say pet quality and bred for CFA. The polydactyl paws kind make me think he's from a breeder. You do see this in other breeds and cross breeds from time to time. Where did your Grandparents get him and how much does he weigh. He looks to be around 18 lbs.
The cat started coming around their house last year when I was visiting over there. I don't know who had him or where he came from.
Babe, as my Grandparents call him, came up to me first. I wanted to bring him home with me but my Uncle said no more cats so I left him there and my Grandparents got attached and started to take care of him.