Long-term feeding of layer feed to roosters can result in visceral gout and kidney failure. Lots of people feed their whole flock layer feed (including the rooster) because it's convenient. But it's hard on the rooster's health. If you intend to cull the rooster fairly quickly (for stew, etc) then go ahead and feed layer feed, but if you want to keep him, do something like what hennible suggested.
Excessive calcium is especially dangerous for chicks under 18 weeks of age. It's also not good for any hen not laying, whether she is not laying due to molt, old age, illness, broodiness, etc.
You can feed chick starter, grower, broiler, turkey broiler, basically any chicken feed other than layer feed. Just keep a small dish of crushed oyster shell (you get it at the feed store) on the side. The chickens who need extra calcium (the hens/pullets currently laying), will eat the oyster shell when they need it. Chicks or roosters may peck at the shell occasionally, but will mostly leave it alone.
I also concur with PRfan that scratch is not a complete feed. If you want more eggs and healthy birds, be sure to feed a complete feed. You can still feed scratch if you want, but as a treat limited to 10% of their diet.
