I want to feed within two to three (max!) months of each bag's mill date, and here it's Purina's Flock Raiser. I've used it for twenty+ years, and it's fine. There are other good choices, it depends on what's available fresh where you shop. And four months old is really pushing it, IMO.
Mary
I feed Purina Flock Raiser, with separate oyster shell. It's fresh (within two months by mill date) where I shop, so our best choice. Once in a while, if the FR is older, I'll buy an unmedicated chick starter to get by. Kalmbach's feed is sold at another store, and held in an outdoor shed...