User blog comment:Giganta/Character Flaws/@comment-5239890-20120708234734/@comment-1038387-20120709184555

He always was slower than Barry. That's not because he's young, or because he's rusty, it's because of the way they got their powers. Jay got them in a freak explosion. Barry reproduced the explosion, under laboratory conditions. That's why he's fastest. Wally used his chemistry set in the garage, and is powers did not manifest until weeks later.

He was already slower in season one - see issue #16, for example, where Barry makes a comment about lapping Wally.