Main Characters:
* Sonic the Hedgehog: 15 years old, but he's been that age for almost 30 years in real-world time! He's a bit of an ageless wonder.
* Tails: 8 years old (though he's also stayed at this age for a very long time).
* Knuckles the Echidna: 16 years old (he's a bit older than Sonic).
* Amy Rose: 12 years old (the youngest of the core group).
* Shadow the Hedgehog: Officially 15 years old, but he was frozen for 50 years before being revived, so his "real" age is much older.
* Rouge the Bat: Age isn't stated, but she's generally assumed to be around 18-20 years old.
* Dr. Eggman: Age isn't stated, but he's depicted as a middle-aged man.
Other Characters:
* Big the Cat: Age isn't stated, but he appears to be in his early 20s.
* Cream the Rabbit: 6 years old.
* Vector the Crocodile: Age isn't stated, but he's depicted as an adult.
* Charmy Bee: Age isn't stated, but he's depicted as a young adult.
* Espio the Chameleon: Age isn't stated, but he's depicted as an adult.
Important Notes:
* Inconsistent Canon: Sonic's story has been told across many mediums with varying levels of continuity. This means ages are often reinterpreted and change between different games, comics, and shows.
* "Ageless" Characters: Sonic and Tails, in particular, are often presented as being a bit "ageless," meaning they don't seem to physically age as much as human characters would over the same amount of time.
If you're curious about a specific character's age, it's always best to look at the source material you're interested in to see how their age is presented there.