Sonic X - 2003 Celebration Aboard the Typhoon 3-13 was released on:
USA: 3 December 2005
Sonic X - 2003 The Space Ship Blue Typhoon 3-2 was released on: USA: 17 September 2005
Sonic Mania is a retro throwback to the classic Sonic games, such as Sonic the Hedgehog 1, 2, 3 & Knuckles, from the Sega Genesis era. Sonic Mania is set to release in 2017.
Sonic the Hedgehog - 1993 Sonic Racer 1-6 was released on: USA: 23 October 1993
Sonic the Hedgehog - 1993 Warp Sonic 1-10 was released on: USA: 20 November 1993
Sonic X - 2003 Worries for Sonic 3-24 was released on: USA: 22 April 2006
Sonic the Hedgehog - 1993 Ultra Sonic 1-3 was released on: USA: 2 October 1993
Sonic the Hedgehog - 1993 Super Sonic 1-5 was released on: USA: 16 October 1993
Sonic Underground - 1999 Sonic Tonic 1-17 was released on: USA: 11 January 2000
Adventures of Sonic the Hedgehog - 1993 Submerged Sonic - 1.26 was released on: USA: 9 September 1993
Sonic Boom - 1974 was released on: USA: March 1976
According to Sonic Jam's Character House, Sonic was actually 16 before the release of Sonic Adventure. So whilst Classic Sonic was indeed young, he's actually one year older than Modern Sonic.
They already have, Sonic 06, Sonic and the black knight, Mario and sonic at the winter Olympics, sonic rivals 1 and 2 and sonic riders zero gravity have Silver as a playable character, except Sonic and the Black Knight has him known as Sir Galahad.