How old is this baby rabbit? what to feed him?

How can i tell the age of a wild cottontail rabbit? it is very young and small it has very small teeth, wide open eyes and fur. he is about 6 1/2 inches long? he doesnt seem to be eating or drinking so we decided to syringe him soft, mushed up excel pellets, and he seems to be eating it.. any help on what to feed him and how old he is? i need as much help as possible! thanks.