User blog comment:Dream Era/Why Sonic has Green Eyes/@comment-477304-20140813030938

I don't believe there's any canonical reason for Sonic or any characters change in the series, it was just a redesign, that's all. Sonic Generations was just a game to celebrate Sonic's anniversary and history, so I don't think classic Sonic's appearance should be taken too seriously.

Also, Sonic was never ten years old in any game.