This is not a "how old is everyone on the site" blog, but rather a blog where you can talk about the ages of the mane six, the pets, the CMC, the royalty, etc.
Personally I think this is how old everyone is according to Pinkie Pride.
Twilight Sparkle: 21
Rainbow Dash: 21 (she has at least 21 candles on her birthday cake in Pinkie Pride)
Rarity: 23 (she seems the oldest in maturity level)
Fluttershy: 22 (stated to be a year older than Pinkie)
Pinkie Pie: 21
Sweetie Belle: 11 (seeems to be the youngest of the Crusaders)
Apple Bloom: 12
Babs Seed: 13
Shining Armor: 34 (he was almost a stallion when Twilight was a filly)
Celestia: 1042 (she's at the very least 1000 years old, and I imagine she was already quite old when she sealed her sister away, though since she's an alicorn, she doesn't age like other ponies do.)
Snails: 13 (he looks to be at least a teenager judging from how lanky he is compared to every other student in Cheerilee's school)
Big McIntosh: 27
Granny Smith: 87
Angel Bunny: 9 (which is adult for a rabbit, though he's probably older if rabbits age the same way as ponies do, in which case I imagine he'd be the same age as Fluttershy if not a little older also he was probably found when Fluttershy came to Ponyville at around 11 or 12.)
Gummy: 2 (he was turning 1 year old when Twilight moved to Ponyville, and I don't think it's been any more than a year yet.)
Opalesence: 9 (she was probably gotten when Rarity moved to Ponyville. This is again adult for a cat.)
Tank: Unknown (he could literally be any age, I'm thinking he's pretty old since he got tired quickly)
Sunset Shimmer: 21
What are your assumptions on the characters ages?