2 way anova

Dear SPSS thinkers,
I have a case with one dependent variable ( image of a product) and two independent variables, gender and age. My problem lies with how to define the variable age when I only want to use the ages between 18 and 30. The survey has been for all ages to 55.
??? is it permitted to SELECT CASES for the age variable and use only the selected cases for the 2 way Anova ( Univariate)?
thanks for your help and advise.