It raised some eyebrows last week when ESPN's Buster Olney reported that free-agent closer Craig Kimbrel is searching for a six-year contract this offseason.
There's nothing wrong with aiming high, and Kimbrel has been an elite closer. But due to how teams view relievers, Kimbrel's age (30), and perhaps even some signs of shakiness in 2018, he may have significant difficulty landing a deal of that length.
• The latest Kimbrel free-agent rumors
Would it really be irresponsible for a club to make that sort of commitment to Kimbrel? While there is no predicting the future in baseball, we can try to learn from the past by looking at how similar players have performed at the same point in their careers.
Now, as Kimbrel's representatives no doubt would argue, it's difficult to find true comps for him. The right-hander rises above the pack, with his 333 career saves ranking first all-time for a pitcher through his age-30 season (Francisco Rodriguez is second, at 294, but wasn't in the closer role at 30). Beyond the saves, Kimbrel has been dominant. His 211 ERA+, 1.96 FIP, and 41.6 percent strikeout rate all rank first in MLB history (minimum 500 innings), as well as first through any pitcher's age-30 season, since the Deadball Era.

With that said, setting minimums of 150 saves and a 130 ERA+ through age 30 creates a solid list of pitchers who enjoyed great success as closers early in their careers. Trimming it further to remove active players (Albertin Chapman and Kenley Jansen, for example) and those who already had fallen off at 30 due to injury or declining performance leaves us with the following dozen (in alphabetical order):
Armando Benitez, John Franco, Goose Gossage, Bryan Harvey, Trevor Hoffman, Robb Nen, Jonathan Papelbon, Mariano Rivera, Lee Smith, Huston Street, Billy Wagner, John Wetteland.
Here is a look at how that group fared, year by year, over their age 31-36 seasons:
At age 31
Averages: 60 G, 65 IP, 35 SV, 2.40 ERA, 6.7 H/9, 2.5 BB/9, 9.9 K/9
Harvey represents the nightmare scenario. After saving 45 games for the expansion Marlins in 1993, he ran into injury problems that limited him to 12 ineffective games in '94 and one final appearance in '95, which preceded Tommy John surgery. The rest of the group ranged from good to excellent, with seven saving at least 40 games and eight producing an ERA+ of at least 165.
At age 32
Averages: 47 G, 53 IP, 25 SV, 3.13 ERA, 7.9 H/9, 2.7 BB/9, 8.7 K/9
This is where the attrition really begins. Besides Harvey, each of Benitez, Franco and Street appeared in 35 games or fewer, with below-average ERAs. Rivera and Wagner threw just 45 games apiece, but with strong results. Nen was terrific for the Giants in both the regular season (2.20 ERA, 43 saves) and postseason (10 games, one run), though he blew the save in Game 6 of the World Series against the Angels. He did it while pitching through a painful shoulder issue that eventually required multiple surgeries and ended his career suddenly at age 32.

At age 33
Averages: 54 G, 58 IP, 31 SV, 2.44 ERA, 7.6 H/9, 2.5 BB/9, 8.1 K/9
Note that these seasonal averages do not account for pitchers who didn't appear at all, which in this case includes Harvey and Nen. It does count Street, who appeared in just four games in 2017, which at this point appears to have been his final season. However, seven of the other nine pitchers logged at least 30 saves, and six had at least a 150 ERA+. In particular, Gossage, Papelbon, Rivera, and Wagner authored dominant performances, combining for a 1.75 ERA in nearly 300 innings.
At age 34
Averages: 60 G, 64 IP, 32 SV, 2.97 ERA, 8.0 H/9, 2.8 BB/9, 8.8 K/9
Street and Wetteland bring the out-of-baseball total to four -- or one-third of the original sample. Benitez lost his closing job in San Francisco and was traded to the Marlins, finishing the year with a 5.36 ERA and nine saves. Gossage also struggled, in a season that signaled the end of his time as a top-level reliever, even though he managed to pitch seven more years. That leaves six pretty effective closers. Hoffman, Rivera, Smith and Wagner all notched at least 38 saves, with Rivera recording a career-high 53 and a 232 ERA+.
At age 35
Averages: 43 G, 45 IP, 23 SV, 2.72 ERA, 7.7 H/9, 2.8 BB/9, 9.0 K/9
Half of the 12 pitchers were either done or barely pitched (Benitez got into eight games in his last taste of the big leagues, and Hoffman got into nine after recovering from shoulder surgery). Papelbon lost the closer role in Washington in 2016, was released that August, and hasn't pitched again. Gossage saved 11 games, and while Smith saved 46, he wasn't especially effective (103 ERA+). Only Franco, Rivera and Wagner remained at or near the top of their game.

At age 36
Averages: 52 G, 53 IP, 31 SV, 2.63 ERA, 7.6 H/9, 2.1 BB/9, 8.0 K/9
Six of the original 12 were out by this point, and Gossage was a shadow of his former self. That leaves five productive closers, and Wagner's 2008 season ended in early August with a torn elbow ligament that required Tommy John surgery. Still, the lefty was one of five in the group who topped 25 saves and a 150 ERA+. That included Hoffman, who made a successful return to form as he regained his health.
At age 37 and beyond
Wagner missed much of 2009 before returning for a last hurrah with the Braves, posting a career-low 1.43 ERA. Smith lasted one more year as a closer, then two more in the Majors. Gossage added five more rather nondescript MLB seasons (plus one in Japan). Franco pitched seven more seasons, though he also lost one due to injury and collected only 65 more saves. Hoffman and Rivera defied the aging curve over and over, both remaining effective into their 40s, with Hoffman breaking Smith's all-time saves record before Rivera took his place.
Summary
With the caveat that the past provides context but no guarantees, there is some encouraging precedent here for Kimbrel -- and his next employer. Hoffman, Rivera and Wagner all remained top closers through age 36 and beyond, aside from the occasional injury. Rivera soon will join Hoffman and Gossage in the Hall of Fame, and Smith could as well, via the Today's Game Era ballot. At least half the group provided four or more good seasons out of the next six.
Of course, it's not all good news. Harvey was essentially done after age 30, neither Benitez nor Street provided much value after 31, and health stopped Nen's stellar career in its tracks after 32.
Kimbrel has been better in his job through age 30 than anyone, but that doesn't make him immune from the ever-present threat of injuries that could knock him out of action and erode the quality of his stuff. Still, history suggests that the club that signs him this winter would have reason to hope for a solid return on investment, if health allows.