As it turns out, there was a bit of script from MLP:FIM that got put out for the episode “Griffon The Brush Off” that listed Applebloom as being seven years old. Allowing for the passage of time (at least two years minimum, as we’ve had two winter seasons pass in continuity, assuming the episodes have any semblance of chronological progression), then it’s been about two or three years since that episode would have taken place in-universe. So the CMC and their peers should be in the 9 to 11 age bracket. At least, that’s the sense it makes to me in my own head.