You can feed him the same as the chicks. It won't hurt him. It's just a higher level of protein. You shouldn't allow him access to layer feed, though. Only layers should eat layer feed, and that extends to your females who may not be laying. The extra calcium in layer feed can and does harm nonlayers... I believe it causes kidney damage, but I may not be remembering correctly. Over time it can kill them.
The easy solution to this is to feed an "all flock" feed and offer calcium (usually crushed oyster shells) on the side. Only the laying females will eat the oyster shells so long as the flock also has access to grit. You can feed chicks all-flock after they're two weeks old.