Bio-Not much is known about Sonic's Past Before he met Tails but some facts are known. It is known that he beat a rabbit called 'Hodgepodge' to Become the fastest Animal on Mobius. He Gets his Speed from his Sneakers but can run fast without them. A while later, He was working out in another Zone and Tails fell on his head. After telling Tails that he is not a bird Tails Joins him in his fight against Robotnik
Notes Relating to the Character-* Sonic has had two On screen Birthdays. In the Episode 'Robotnik land', Robotnik noticed in the paper that it was Sonic's Birthday and tricked him into 'Robotnik land' while Tails was getting a few friends together for a party. In 'Tails Prevails', Tails becomes an inventor by making Sonic a flying Bike for his Birthday and gives it to him at his party. Sonic there for should be 2 years older then the start.
* We don't have an official source for Sonic's age apart from guess work. We know Sonic is a teenager, due to Catty Carlisle's 'Sonic's Song' calling him a Teenager. Also, in One episode, it was commented about he should be in school, so this puts Sonic between 12 and 19. Sonic has two birthdays in the show and nothing seams to really show him ageing that much, so we can say he is still a teen at the end of the show, meaning about 17 at the start of the series seams right. Having Sonic in the 19s at the end, however, does seam to make him a bit old for the kind of cartoon this is. They mostly want Sonic to be like a big brother to the target audience, so it seams, if we count his two birthdays, Sonic would be about 16 at the end, being 14 at the start. This would fit all known facts and the target group.