Well, in the real world yes. But Sonic is only about 16-17 in-game. (if you count the one year time skip in Sonic Chronicles, and Sonic's B-Day Picnic in Sonic Generations.)
But Sonic Chronicles wasn't even developed by SEGA... Also, didn't SEGA say that supposedly Sonic was supposed to be 15 y/o forever...until Sonic Generations? 0.o
For God's sake, Sonic is supposed to be fifteen years old forever, all right? He even turned fifteen in Sonic Generations and in that episode of Adventures Of Sonic The Hedgehog.