I've recently added a bunch of girls hats to my shop and for the first time I've got options for the age ranges the hats will fit. I've added each age as a tag but that takes up so many tags I wonder if it's necessary/worth it?
You would have to do the research to see how often people search for age ranges with your kinds of item. The google keyword planner might help, and Etsy's suggested search might help. Then try it out on a few listings first to see if it is working.