As some have said, a yearling boa should be on at least pup sized small rats by now. My 07's are all eating small-mediums, some are on larges. My 08's are all eating medium-large mice. I have in the past always fed rats from birth on up to my baby boas, but I'm going to be feeding mice to them this year because I've noticed that the fat content in rats makes for "pudgy" looking baby boas until they start to gain their size more. With mice they get a leaner more healthy look and seem to develop muscle tone faster too. I'll be keeping my baby boas on mice until they are ready for pup rats starting this year.

Sorry, I went off topic, lol. Your boa should be eating (at the minimum) large mice at a year old, BUT it does all depend on what kind of boa you have. If you have a central american or nic boa, they don't grow so fast and could easily be on small-medium mice still. Still a little small, but not nothing to worry too much about.

Do you have any pics?