I'm a geeky Sonic nerd...
Some of these questions have answers that have changed over the years, or change depending on which language you play the game in. :P Like, Sonic says both "Sayonara, Shadow" and "Adios, Shadow" - he says Sayonara if you have it in english, Adios if you have it in Japanese.
Eggman's IQ was stated to be "over 200" at one time, because that's the highest the IQ test would go.
Sonic's age is in a constant state of flux so one game might say he's 16, another will say he's 15.
So on and so forth.