Look toward the top of any list of free agents available this offseason and you'll find Jason Heyward's name. There are good reasons for this. Sure, he's polite at parties, never leaves the seat up and always holds the door open for the elderly, but it's more than that.

He's got perhaps the most well-rounded set of skills the free-agent market has ever seen. He's got a career wRC+ of 118, so he can hit, he's got some power as well as on-base ability, he's an excellent baserunner, and he's a superb fielder. There's really nothing that Heyward doesn't do well, and when you add his age into the equation that's when things get silly, financially speaking. Ah, his age. That's really the crux of this whole thing.

Heyward is 26, so unlike the case with most free agents, the team that signs him will get his peak seasons. There are some players who have many of Heyward's abilities but who won't approach the contract he is expected to get. Ben Zobrist, for instance, is an interesting comparison. He's a good fielder, a smart baserunner, he has some pop in his bat and he's exhibited about as much on-base ability as Heyward has. He also plays 70 positions despite baseball not having that many. But Zobrist was born in May 1981, meaning he'll be 35 years old next season. Heyward was born in August 1989, so he'll be 27. This is why Zobrist just signed with the Cubs for four years and $56 million while Heyward is expected to more than double both the total years as well as the average annual value of Zobrist's contract. Imagine if you could go back in time and sign Zobrist for 10 years beginning at his age-26 season. In today's market that would be a bargain.

Clearly, Heyward is an extremely talented player, and his age makes him that much more attractive. You don't get $200 million contract offers if you aren't. But the issue isn't how good he's been, but as is always the case with free agents, it's how good he'll be. The thing is, Heyward is good at many different aspects of the sport.

The easy thing is to look at Heyward and say, "He has so many skills, he'll be good for a long time." However, it's the players with one great skill who have further to fall. Take the case of Carl Crawford. When he signed in Boston he was 28. He had put up 5.9 and 7.7 WAR totals in his previous two years. In the six seasons since, he's been worth 6.1 wins in total. Most alarmingly, all of his skills have declined almost evenly. His power has dropped, as have his ability to hit for average and get on base. His great base-running became good or average base-running. His incredible defense disappeared to the point where he hasn't added much value (if any) defensively.

Heyward isn't Crawford, but there are parallels -- and perhaps the most disturbing is his reliance on defense for a large portion of his value. It's not that defense isn't important. It is. But we're also not great at measuring it, and that is a problem (presumably teams do a somewhat better job). But mostly the problem is that defense doesn't tend to age supremely well. This isn't to say that Heyward will be a bad defensive player in five seasons, but that he might be only a tick above average as opposed to an elite. And outfielders who are a tick above average with some on-base ability and not much power aren't exactly $25 million per year assets.

Heyward partially offsets those worries with age, in the sense that his offense might improve at which point the worries about his defense not aging well would be offset or simply invalidated. Heyward is a big guy, and he's quite strong. There is power in the body. The issue is accessing it. Some players are big and strong and they don't hit for power anyway. Think Sean Casey. Heyward isn't Casey, not by a long shot, but Heyward has slugged .431 for his career. In this offensive environment that's quite good, but it's not far off from unexciting. A small dip would be a large problem, and Heyward actually had more than a small dip just two seasons ago, slugging .384 in 2014.

The danger with Heyward is if his offense never improves from where it is now -- in the good to very good range -- and then all his skills degrade with age. That might sound farfetched, but it's exactly what happened to Crawford. Crawford is still a decent player, with some pop and some ability to cover the outfield corners, but he's now being paid lots of money to be the player he was five years ago -- not the player he is now.

We all lose to time eventually. Baseball players' skills degrade in a roughly predictable window of time. That's fine if you're talking in abstracts, but when focused on a specific player, there's a big difference between how Crawford aged and how, say, Kenny Lofton or Ken Griffey Jr. aged. The first wasn't worth a free-agent contract covering him until age 35, but the second both were.

Heyward's skill set isn't unique, but it's very difficult to find. While teams might be dreaming on his age a bit, even if they're disappointed and he has already reached his peak, his many skills on the field will make him a valuable player into his 30s. And because he's only 26, that's a fair bit of time. But if he doesn't improve on offense, there is some chance he becomes an average to slightly above-average outfielder with an amazing contract. Still, the chances that Heyward is worth his contract between now and his age-30 season are very high. And for a free agent, even one who depends on defensive value to the extent Heyward does, that's a low-danger investment. For a team looking to win now, that in and of itself might be enough to take the plunge.