Board Thread:Speculation, Theories, and Rumors./@comment-24261123-20140201151719/@comment-477304-20140505234240

You should get that cough checked out, you might have something.

The birthday leaves Sonic's age a mystery, and all we can assume is that he's still 15. Sonic Jam, the only source for Classic Sonic's age, list him as 16, so I wouldn't put too much thought into anything regarding Sonic's age.