I'm not bashing Darvish - I thought the Twins should have beat Chicago's offer and signed him (provided he wanted to sign here at all) - but a variety of pitches does not negate aging. Good pitches are good pitches; bad pitches are bad pitches. If Darvish loses 2-3 mph on his fastball, he'll likely lose 2-3 mph on the rest of his pitches as well, along with some movement. He wouldn't only lose a good fastball, it's likely that he'd also lose a few other good pitches as well. Again, not arguing whether the Twins should have offered more, only arguing that Darvish's arsenal will prevent him from getting old, just like everybody else. The pitchers who succeed as they age either maintain velocity, gain more command, or make an adjustment and change their approach. As far as I know, there's no way to predict any of those things happening to any specific pitcher.