As a humanization artist, Kirby in clothing some would consider feminine is pretty fun to draw. However, Kirby in canon, I believe, actually has no gender, which I fully support.
Well, no where does it say Kirby is female, so we're all good on him not being a girl and being either a boy or nonbinary, though seriously, just because something/someone is pink and/or has a high pitched voice doesn't automatically make it female.