He is definitely up there age wise! Congratulations on good husbandry. He may be falling due to age, but I am not that experienced with older chameleons. However I have read about younger chams with MBD doing a lot of falling. My first cham had MBD and had a lot of difficulty with walking, he would grab his front legs with his back feet causing him to fall. I kept him in a much lower enclosure. I recall that some folks actually turned their tall enclosures on their sides so there is less height to fall from. They also lined the bottoms with soft towels. It is hard to watch a pet decline. I think it is encouraging that he still eats and drinks. Pete did not do that very well toward the end of his life. Good luck with your boy. You may want to go to the vet to rule out other problems as well.