An animal that has been an indoor cat for so long is no longer equipped to survive outside. Other cats will fight with him for safe areas to sleep. They will also fight with him for food. Outdoors is dangerous for an indoor animal which will include exposure to Feline Aids and Feline Leukemia along with mosquitoes, fleas, and ticks that carry diseases. If you cannot keep your cat inside, I suggest that you find someone else to take your cat or bring him to a no-kill shelter. If you must put him outside, be sure to provide him with a safe place to sleep (such as on a closed porch), food so he doesn't have to hunt and get him all of his shots and treatments to keep him as safe as possible.