As Matt Holliday enters his age-35 season (his sixth full season with St. Louis), one can reasonably wonder the effect age has had (and will continue to have) on his overall performance, particularly while he is still under contract with the Cardinals (there is a 2017 club option for $17 million with a $1 million buyout). Projection systems have understandably had Holliday on a slight decline for a few years now (BABIP- and age-related), but he has managed to outperform the majority of these projections. In fact, in terms of wRC+, Holliday has been the best hitter on the team in each of the last three seasons, and ZiPS projects him to take this "crown" once again in 2015 (.359 wOBA; Jason Heyward comes in second at .344)
So, what effect has age had on his performance over the years? The obvious thing to look at first is durability. As the human body ages, it tends to break down more regularly, and the recovery period after a breakdown usually takes longer. However, since being acquired by the Cardinals in 2009, Holliday has played more games than any left fielder in baseball (892), and this includes 2011—a year in which he dealt with a wide array of injuries (appendectomy, thigh, back, finger) all season. Heck, if you expand the search and include all MLB outfielders, only four have appeared in more games than Holliday: Hunter Pence (953), Ichiro Suzuki (924), Adam Jones (900), and Nick Markakis (900). Thus, up to this point, durability has not been an issue for Holliday, and given his dedication to training (links to a 2010 Muscle & Fitness video, workout starts at ~0:48), this really is no surprise.
Durability hasn't been an issue, but what about bat speed? That has to be declining, right? It's almost certainly true that Holliday's bat has slowed down in recent seasons, but without regular access to bat speeds or even ball exit speeds, it is virtually impossible to quantify by how much. Sure, Fox Sports Midwest provides us with ball exit speeds on various hits throughout the season (as seen in the embedded video below), but unfortunately, it is not a regular feature, and there is no database we can scour, either.
Dan McLaughlin, "Holy smokes! That is undoubtedly the hardest ball I have ever seen hit into Big Mac Land. No question about it." Ricky Horton added, "110 MPH off the bat of Matt Holliday." And from Mike Shannon, "Swing! And it's 3-0 Cardinals. Look at this baby fly! Woohoo! Big Mac Land...What a rocket that was, Mike. Hoo!" A quick glance at BrooksBaseball shows that Jorge De La Rosa threw a relatively well located (down and in) 93.5 MPH fastball. A pitch of this velocity and that location can be troublesome for some hitters with declining bat speeds, but Holliday clearly didn't have an issue with it. Though, to be fair, Holliday was ahead in the count (2-1), and with two runners on base, he was able to look for a pitch to drive, and this is exactly what he did.
One at bat is nowhere near the sample size needed to determine whether or not a decline in bat speed is having a negative effect on Holliday's performance. Thus, using Daren Wilman's terrific Baseball Savant website, I compiled data on how Holliday has performed on 93+ MPH pitches over the last seven seasons (2008 is the earliest season available). For comparative purposes, it is probably prudent to "throw out" 2011 as he was hampered by injuries all season long and played in less games than normal.
In terms of hits (the red line), Holliday has remained steady on pitches 93 MPH or faster. Hits don't tell the whole story, so I included swings and misses (aka whiffs; the blue line) as well. As with hits, Holliday's whiffs have held relatively steady over the years as well. Indeed, he had a pretty significant increase in whiffs last season (up to 62, from 47 in 2013), but a brief look at the location of these pitches provides a possible reason behind the increase:
With roughly 50% (29/62) of his whiffs occurring on pitches out of the strike zone, this appears to be more of an "approach" issue than a "bat speed" issue, and it is something he has dealt with just fine over the course of his career. The down-and-in zone has the most whiffs (11), but this has been one of his hottest zones when looking at results, so there are no complaints here.
Matt Holliday is not getting any younger, but in terms of durability and bat speed, he has yet to show much of a decline. I am clearly biased and it may sound foolish, but I do not envision much of a decline in 2015, either. In fact, with the addition of Heyward (hopefully hitting in front of him in the two-hole), I wouldn't be all that surprised if Holliday actually performs better in 2015 than he did in 2014. If you haven't yet listened to Episode 14 of the Viva El Birdos Podcast, Ben tends to agree with this assessment of Holliday's 2015.