In my Sonic X AU, Shadow was created by Gerald, same as the main canon, but he is also able to age over time. Shadow, in this image, is 16 and in his second year of high school, whereas Sonic is 15 and is in his first year.

Due to their adoptive mothers having a close friendship with one another, Sonic and Shadow grew up together and became good friends instead of rivals.

Anyway though, in this image, the boys challenge each other to a race, on their way to a typical day of high school x3

Background/Sonic and Shadow © SEGA