It should be straightforward, but it is not possible to deduce from your code how to do it. In particular, since none of your variables mention age, and there is no annotation mentioning it, we can't figure out how to apply the restriction you want.
Can you upload the data needed to run the code, and identify the age?
That being said, if CarsCasesFemale1(:,1) is the age variable, which seems possible, then I think this does what you want.
isFemaleUnder19 = femaleCases1(:,1) < 19;
and analogous code for males.
Even if it doesn't do what you want, maybe you can see the logic, and figure it out.