Curate, connect, and discover
Take the average age that a cis child would start the puberty you are now undergoing. If you'd like, you can use a sibling or other relative's starting age to guess at what yours would've been. Keep in mind that hormonal shifts start a while before any changes are readily apparent, so the actual starting age is younger than you might guess.
Determine the amount of years you've been on hormones. Subtract any amount of time you weren't able to consistently keep up with it. If you went through a period of significant dose adjustment, you may want to set your starting clock at when you got on the right dose for you, not when you started trying it out.
Add Steps 1 and 2 together to get your True Gender Age.
Compare your changes to cis people of that age, not people your own age.