Kirby has to be young, because Meta Knight is of the same species (pretty sure this is according to canon), and Meta Knight is a star warrior who is much older, more mature, which is why he looks different.
I always thought that the Star Warriors started out as a blank slate, then gained a distinctive look as they absorbed different abilities, which would explain Meta Knight, who favored blade abilities, but then Kirby is still in the blank slate phase
He's also only supposed to be 8-inches high, according to the original Smash Bros instruction manual

Monster Hunter: pissing me off since 2010.







