Jan 6 Age of the Mane 6 · 6:05am Jan 7th, 2017
I am not quite Sheldon (from Big Bang Theory) Class fussy. However, I damn near demanded my money back & walked out of Star Wars because Han Solo used "light week" as a measure of time not distance. I did refuse to see or buy the 25th anniversary release (in part) because I heard they did not correct this misuse. I very seldom watch scifi on TV or in movies because I love it & it burns my biscuits to see how poorly they do it.
I love MLP & it irks me not to know what chronological order the episodes belong in. So, I'm going to start by putting the 1st 3 seasons in what I think is the right order. This starts with "What age are the Mane 6?". This in turn partially hinges on the question "When did the events in The Cutie Mark Chronicles (S1 E23) occur?"
I think they happened late May or early June 10-12 years before the pilot. Twilight was applying for Celestia's school, so it was after the end of the Spring semester & before the start of the Fall semester. Spike's birthday in Secret of My Excess was his 1st in Ponyville, so before June 19th.
IMO, Dash was 17 during the pilot & AJ was 25 (I'll explain why next blog). 12 years back makes Dash 5 years old when she did the 1st rainboom & was the 1st in her class to get her Cutie Mark. It makes AJ 13 when she went alone to Manehatten & was the last in her class to get her Cutie Mark. Plus, TCMC does not show AJ's parents so it seems likely that they were already gone. This means that Apple Bloom must already have been born & was 12+ at the time of the pilot. So, it's unlikely to have been more than 12 years ago.
Twilight was applying for school so she was 4-6 years old (depending on whether it was kindergarten or 1st grade). 10 years means she was 14-16 years old during the pilot. So, it's unlikely to have been less than 10 years ago.
So, my final answer is "these events occurred 11 years before the pilot".