Saito didn't pitch in Major League Baseball until he was 36. But among the 69 pure relief pitchers who threw at least 250 innings from 2007 through yesterday, Saito ranks 4th in ERA and 11th in strikeout-to-walk ratio. He's been really good.
He's also 42, and hasn't pitched well for the D'backs yet. I'm not giving up on him, though.