Since I teach, I can only nudge you in the appropriate direction
Select by attributes will allow you to query the cases by age
Select by spatial location allows similar functionality but allows for a distance option
Intersect will allow you to delineate space around your schools and a join by spatial location will allow you to further delineate age cases
There are other options
At this juncture, it would be best for you to experiment and report on successes and/or failures so you can be nudged further to a complete set of answers obtained on your own