While we prize film study above all when evaluating prospects, we also try to incorporate analytics and metrics into our process. Any information we think we can obtain that actually correlates with determining whether a prospect will succeed or fail in the NFL is good information.

I was thinking about this recently in terms of quarterback evaluation. For nearly a year now, we’ve expected Deshaun Watson to be the top QB prospect (and likely the top pick) in the draft, but now he may have challengers to his throne.

One of those challengers is Mitch Trubisky. And while I like some things I see on film, there’s a metric aspect that seriously concerns me. Namely, this:

Mitch Trubisky is at least a year older than every other top QB prospect in this draft, and he only has one year of starting experience.

I’m not the first to tell you that starting experience is important in terms of how a quarterback will develop. What I will tell you is something less obvious. Everyone sees the obvious connection: The more you start, the more experience you get; the more experience you get, the better you get at what you do.

But there’s a second, hidden side to why starting experience is so important, especially starting experience from a young age:

A dude who is good enough to start at a major college program at 18 or 19, is likely to make a better pro than a dude who isn’t good enough to start until he’s 22. (When you consider how QBs continue to develop throughout their careers– good ones peak in their late 20s, great ones in their early 30s– think about the difference that three years of development makes.)

Deshaun Watson began to get a few games’ starting experience as a 19-year-old freshman at Clemson, before moving full-time into the role as a sophomore and junior (and, it’s worth mentioning, going to two national championship games and winning one in those two years).

Patrick Mahomes backed up Davis Webb for Texas Tech as a 19-year-old freshman, before beating out Webb as a sophomore (Webb was a junior and transferred to Cal for his senior year) and starting for two years before declaring.

Brad Kaaya has been a three-year starter for Miami since he was a 19-year-old freshman.

DeShone Kizer beat Malik Zaire for the Notre Dame starting job as a 19-year-old redshirt freshman, and started for two years before declaring.

Mitch Trubisky redshirted as a 19-year-old freshman, then backed up Marquise Williams for two years. (Williams, by the way, went undrafted and couldn’t make the Packers’ 53-man roster.) Now he has one year of starting experience as a 22-year-old redshirt junior– and one where his numbers still weren’t as good as some of the younger guys like Mahomes and Watson.

There are things to like about Trubisky. (If you watched the Sun Bowl, Trubisky’s comeback drive attempt is a great example: He doesn’t get fazed by the hits or his receivers’ drops and repeatedly delivers on-the-money deep balls.) But it’s also likely he has less room to grow than the other prospects, and that means his ceiling is lower– maybe not what you want from a guy you’re looking at taking in the top of the draft.

While age has certain limitations as far as evaluation goes– a good player is a good player, and a bad player is a bad player, and teams really can’t count on anything beyond the four or five years they have a player on a rookie contract– when you’re taking young players and projecting growth is an important part of your decision, age matters.

Age is why, for example, I’m much more worried about Josh Doctson’s inability to get on the field in 2016 than Laquon Treadwell’s. Doctson is two and a half years older than Treadwell. Of course, like I said, talent is talent– Michael Thomas was nearly as old as Doctson, but he stepped in right away and put up one of the best rookie seasons in history. (Fun fact: Thomas is six months older than Brandin Cooks, who just completed his third season for the Saints.)

If you’re similarly concerned about age in receivers for the 2017 draft: Did you know Dede Westbrook is three years older than JuJu Smith-Schuster? You do now.

Anyway, a good player is a good player regardless of age, but since very few NFL draft prospects step in right away and play at a high level, some expectation of development is required. And a younger player always has more room to grow than an older player. And a player good enough to start at a young age is almost certainly going to be more talented than a player who couldn’t start for two or three years.