How old can a baby be to start sleeping with a crib bumper inside the crib? My son rolls around like…

How old can a baby be to start sleeping with a crib bumper inside the crib? My son rolls around like a crazy man in his crib at night. Often times I find him up against the crib with his arm through the rail so if it's not safe I don't want to put it in but maybe it would stop him from being in such awkward positions