Unfortunately the safest thing to do is put him in a bed (or mattress on the floor if you think he'll fall out). Once he is old enough to climb out, he is old enough for a bed. You don't want to risk him falling and hurting himself (or pulling the crib down on top of him). My oldest girl didn't climb out until she was 2 1/2, my oldest boy NEVER climbed out on his own, and my other daughter climbed out at 20 months. I'm sure my youngest will climb out by 15 months--he is already 33" tall at 10 months! All that to say, the climbing age varies.
With our children, we took everything out of their room except their bed and a couple of stuffed animals (without any buttons or anything that could come off for choking hazards) and locked the closet door so they couldn't play in there (we have large closets so we put their dressers in there). Eventually he will learn he needs to sleep when he is in his room and you can gradually start adding things back in...
Oh...just a thought...before converting to a bed, make sure he is climbing out without ANYTHING in his crib (no pillows, crib bumpers, stuffed animals, etc.)...that may by you some time MAYBE....