Nothing I say below is going to be new to anyone here. Just consider it a reminder.

I was looking at the list of 2023-24 free agents and the most intriguing name on it was Matt Chapman. He's an excellent player who'll probably end up producing 5 fWAR this year (13 over the last three years, his age 28-30 seasons). But if we were to sign someone like that, what could we reasonably expect from him going forward?

I ran a search for every player who posted more than 10 fWAR in their age 28-30 seasons between 2013 and 2019. (I used Fangraphs just because I find their search page to be easier to navigate.) There were 22 search hits. Here's what these 22 guys did in their age 31-33 seasons.

Age 31: Mean 2.8 fWAR, Median 2.5 fWAR
Age 32: Mean 1.9 fWAR, Median 1.4 fWAR
Age 33: Mean 1.4 fWAR, Median 1.2 fWAR

Not great.

If we make the criteria a little stricter and set the minimum at 11 fWAR from ages 28-30, we get 16 search hits with the following results:

Age 31: Mean 3.1 fWAR, Median 3.1 fWAR
Age 32: Mean 2.0 fWAR, Median 1.7 fWAR
Age 33: Mean 1.5 fWAR, Median 1.4 fWAR

A little better, but still pretty grim. And the results don't get any better (arguably they get worse) if you set the minimum at 12 fWAR.

The lesson's pretty clear. We're not in the steroid era anymore. Players usually decline pretty fast once they get past age 30.

Of the eight regulars in the Phillies' lineup (excluding 1B since there's no set starter there), five are 30 or older. Combined, they make over $110 million per year.

1. J.T. Realmuto is 32. Going by fWAR, last year was the best year of career (6.5). But he didn't have a great first half in 2023 and is currently on pace for ~2.0 fWAR. I'm not saying he's cooked or will never have a great year again. But the broad trajectory of his career is pointing downward.
   
   
2. We signed Kyle Schwarber to a four-year contract after his age 28 season, 2021, which was the best year of his career (2.8 fWAR). So far in 2023, his fWAR is negative. Much of that is due to his atrocious defense. But he isn't that great of an offensive player either. If you projected his career-average hitting stats over a full season as DH, he'd generate less than 2 WAR. And it's more likely than not that he'll underperform his career averages over the remainder of his contract.
   
   
3. Nick Castellanos is having a nice bounce-back campaign this year at age 31. I think we can say his poor 2022 was a fluke. But his career-high in fWAR is 3.6, which he posted at age 30 in 2021. I don't think you can reasonably expect him to average more than 3.0/year over the remainder of his contract.
   
   
4. Trea Turner's subpar first half is probably a fluke. But he's 30, and you can't expect him to average more than 6 fWAR (as he did in 2020-22) over even the next few seasons, let alone all ten remaining years on his contract. If he averages more than 4 WAR in 2024-2026, we should consider ourselves fortunate.
   
   
5. Bryce Harper is a special player and maybe the normal rules of aging don't apply to him. At the same time, he's had a grand total of two seasons in his twelve-year career when he's posted more than 5 fWAR. And while his recent injuries seem flukish, what if they aren't?

The day is coming, sooner than any of us hope, when those five guys won't merely be overpaid - their collective level of production will be outright mediocre at best. Good teams don't win by relying on guys who are past their primes. I wouldn't say these guys are past their primes yet, but every one of them is likely past his peak. And all of their primes will be over sooner rather than later.

There are two ways you can react to this. First, you can assume that crashing and burning is inevitable, and you can keep doubling and tripling down by liquidating more and more future assets and instead investing resources in aging "names." Second, you can try to right the ship in midstream and develop some younger talent now before it's too late. I would choose Option #2, even though there's no guarantee that it will work. It's worth the risk. Option #1 will almost certainly lead to misery, as it did from 2012-2017 and 1984-2000.

What does that mean in practice? One, it means being very circumspect about trading prospects for vets at the deadline. Pull the trigger only if the trade is a clear-cut win.

Two, I think it means committing to your younger players, even if they are flawed. Minor league prospects are great, but in some ways there is no better prospect in baseball than a guy who is able to hold his own in the big leagues before reaching prime age. Bryson Stott is on pace for ~3.5 fWAR this year. It's a nice season, but he's clearly inferior to someone like Matt Chapman. But who's likelier to be more productive from 2024-2026? The answer is Stott, just because he's 25 and likely to get better, while Chapman is likely to get worse. Will Stott ever reach the level of prime Chapman? Maybe not. But he has a better chance to do it than 33-year-old Matt Chapman will.

Stott's an easy example, but the rubber really hits the road with someone like Alec Bohm, who clearly isn't a good player and doesn't appear to be improving very much. But I'd say you should still take the plunge. One thing I realized when running the searches above is that several of these guys who were elite in their late 20s were pretty bad in their mid-20s. D.J. LeMahieu produced 0.9 fWAR/150 in his age 24-26 seasons, then broke out at age 27. Brian Dozier had a negative fWAR in his age-25 rookie season, then was decent at 26 and outstanding from 27-30. Charlie Blackmon averaged 1.7 fWAR/150 at 24-26 and 4.8 at 29-30. Whit Merrifield at age 25 was slashing .265/.317/.364 in AAA!

It wouldn't be a bad strategy for a team to just blindly acquire as many 25-year-olds as possible, coach them up, and hope some of them improve. The probability of success is not terrible. I wouldn't bet money on Bohm becoming a solid big league starter by age 28 (let alone an all-star like LeMahieu or Dozier) but I do think that outcome is no less likely than, say, Tyler Black or Jacob Berry becoming solid big league starters by age 28, and those guys are very good prospects.

In short: (1) Player development is essential if you want to have sustained success as a baseball team. (2) Player development doesn't only happen in the minors. It extends to pre-prime major leaguers too. (3) You can't be good at player development unless you're willing to take some risks and commit to guys who might struggle or ultimately fail. Any team can "develop" guys who "get it" from day one. What sets the best organizations apart is their ability to develop guys who don't get it from day one. (4) The alternative is guaranteed eventual failure. Father Time, as they say, is undefeated.