Both of my cats have medium length hair.. and they have NEVER been to the groomers. Their fur stays imaculate! Cats are WAY better at taking care of themselves and grooming themselves than dogs are. Yours may never need groomed, if he takes good care of himself. Help him out and brush him a couple times a week.. Then just play it by ear.. if he needs it.. take him!
Some cats are better than others about keeping their fur groomed. I second Jocey's suggestion for brushing once or twice a week - if you start when they're small they shouldn't have a problem with it. If you stay on top of it, you shouldn't have to go to the groomers. If you don't brush for awhile (and have a lazy cat) they can develop mats that a groomer will need to cut/shave off.
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To be yourself in a world that is constantly trying to make you something else is the greatest accomplishment ~ {Ralph Waldo Emerson}