Have you thought about assigning different numbers to each of the radio buttons and have a minimum value when it returns? If it returns 0 or NULL then display a message? So youth group could be something like.
YOUTH
[checkbox] 5 - 8 (value 1)
[checkbox] 9 - 12 (value 2)
[checkbox] 12 - 16 (value 3)
etc you get the point.
That way if it returns 2 then you know it’s the 9-12 group. You could store any of the checkbox group results to the same variable and check that.