Let N=number of time eat our per week (1.le.N.lt.10)

Let BY= year of your birth

(2N+5)*50 + 1758 - BY

100N + 250 + 1758 - BY

100N + 2008 - BY

Obviously, 2008-BY is your age, N is the first digit of the resulting 3 digit number.

Changing 1758 to 1759 will make it work in 2009, etc.