My 1 1/2 year old cat still nurses his food?

Well, I have a 1 1/2 year old Maine Coon mix that pretty much nurses his food. He will get a piece of cat food in his mouth, put his mouth against the side of the bowl, and just suck on the cat food until he thinks it is soft enough, and of course, then he swallows it. This is obviously not normal (or at least, I doubt it) Not sure if this has anything to do with it, but we found him in a barn out in the middle of no where along with several other cats, but no mom. Do you have any idea why he does this?