Felix Hernandez has been historically excellent as a youngster, ranking 15th all-time in Wins Above Replacement among starting pitchers through age 26. He also has a lot of mileage on his golden right arm. Hernandez has thrown 1,620 innings in the majors so far, the highest total for an Expansion-Era pitcher through age 26 since Dwight Gooden tossed 1,713 frames from 1984-1991.
With Hernandez on the verge of signing a contract extension that will keep him in Seattle through the 2019 season at a cool $175 million, it's worth asking: How have other pitching phenoms fared in their later years? Do they keep on racking up Cy Youngs, or do they crash and burn? Unfortunately, the answer isn't nearly that neat and tidy. History suggests that Felix could be anything from an inner-circle Hall-of-Famer to a guy who has to buy his own ticket into Cooperstown.
Using Baseball-Reference's Player Index tool, I made a list of Expansion-Era starting pitchers who accumulated between 25 and 35 Wins Above Replacement through their age-26 seasons. Hernandez has 31.5 through age 26, so these guys were in the same ballpark as the King. Here's the list, with WAR totals before and after age 26:
You can't get a much wider range of outcomes than this. Tom Seaver remained a workhorse into his early forties. So did Roger Clemens, either through a Nolan Ryan-esque work ethic or a willingness to turn himself into a science experiment, depending upon whom you ask. Pedro dominated into his early thirties before breaking down physically.
On the opposite end of the spectrum, Jim Maloney suffered numerous shoulder and arm injuries before tearing his Achilles trying to leg out a hit. He threw his last pitch at age 31. Dean Chance lost his fastball and was out of the game at age 30. Doc Gooden was done as a durable, productive starter by 28, though he hung around through injury and substance abuse problems long enough to throw a no-hitter and capture a pair of World Series rings with the Yankees.
Will King Felix's career turn out like Tom Terrific's, or Doc Gooden's (minus the legal run-ins)? I have no idea, but that's the $175 million question.