Sounds like you've specified the field to a date data type. That's going to require the full date, not just the year. You can change it to a number or text data type, or just enter 1/1/1974, or some other arbritrary date. If it were me, I'd probably do the latter since it sounds like you have some complete date data. If you want to perform functions on that date field later, like buidling a report of average number of books read in every month of the year, you're going to want that to be a date data type.

HTH

Disclaimer: I don't and won't use Access, I'm speaking from general database design experience.