Cochran's I'd say. That's where I learned.

For looking at age breakdown of town, city, and village populations, go to the census website. Here's an example for Richmond village : https://data.census.gov/cedsci/profile?g=1600000US5059200

You just scroll down to the populations and people section. You can search by town, city, CDP/Village, County, State, etc.

Edit: For some reason when I first wrote this it looked like it was written by someone who barely knew english.