A while ago, an early script from “Applebuck Season” described Apple Bloom as being 7. So I kinda based the CMC’s ages on that.
From there, I started calculating time in Season 1.
Apple harvest season is usually in late summer and early fall, around September.
I went with the idea that Season 1 lasted for about a year between Summer 2010 and Spring 2011. Since AB’s set birthday in PC is in October, that means she’s 8 by the time Season 2 starts.
When S2 ends (with it being Summer 2012), she’ll be 9. And this is where PC begins. By the end of 2012, she’s 10.
By the end of 2015 (3 years later), she’s 13. And since it’s March 2016 in PC right now, she’s still 13.
(Here’s a rough rundown I made a while ago.)