Problem with using parameter in query with calculation from date

I have a database with a Date of Birth field. I have a query with a field that calculates the age from the Date of Birth (DateDiff("yyyy",[Date of Birth],Date())+Int(Format(Date(),"mmdd")



As a criteria in this field I want to be able to select a minimum age, so >=[please input minimum age]



However the results are bizarre - sometimes it gives the right answer, and sometimes not. It seems to have a particular problem with ages above 10, which show up all the time.



Could anyone help?



Thanks in advance

Problem with using parameter in query with calculation from date