Typically the number that concerns fans when a free agent is signed is the one that follows the dollar sign. But when the Steelers signed Darius Slay to a one-year, $10-million contract, his 34 years of age sent up red flags everywhere.

After reviewing the film, age really does seem to be just a number with Slay.

Throughout his career, Slay has been a phenomenal in man coverage. That's the main reason why over a 12-year career, Slay has made six Pro Bowls, one first-team All-Pro and recorded 18 interceptions and 160 passes defensed. He quickly became a very smart player who learned how to marry athleticism, quickness and elite speed (4.36 40-yard dash at the Combine) with great technique and anticipation.

Of course, as any player ages, they slow down. That's the primary concern among those skeptical of adding Slay to the mix now. There were several younger, high-profile cornerbacks available in free agency, but the Steelers went with Slay on a one-year deal. That not only shows a vote of confidence in Joey Porter Jr., but also Cory Trice Jr., both of whom could greatly benefit from Slay being in the defensive backs room.

There's also a perception that the 34-year-old cornerback is on the decline. Some may even point to the goose egg in the interception column in 2024, the first time Slay has not recorded a pick in the regular season since he was a rookie in 2013.

However, after studying several games, Slay can absolutely still play.

The first thing that jumps off the tape is Slay's ability to still read and react to the quarterback, receiver and the play as a whole:

Here (bottom of the screen), Slay is responsible for whichever receiver winds up on the outside. He uses elite instincts to jump on the in-breaking route to break up the pass. This ball isn't thrown very late, nor is it inaccurate. It's just a great play by Slay.

This is a different type of play that shows Slay's ability to snuff something out because of his instincts (top of the screen). He does a great job of dissecting the play ahead of when the tight end can get to him for the block. Because of that, he slips past him and gets a tackle for loss.

This shows what Slay can do in zone coverage (bottom of the screen). On this play, he's responsible for the curl/flat zone. When the receiver runs past him, he passes him off to the safety behind him and keeps his eyes forward. By the time Jayden Daniels starts his throwing motion, Slay is roughly 12 yards away from Jeremy McNichols, but his reaction time allows him to close in and make the tackle for a 1-yard gain on a critical third-and-5 play.

A big reason why Slay's play hasn't deteriorated as he's aged is because of a fervent dedication to film study. He was taught that when he was younger by Teryl Austin, who was his defensive coordinator for four years in Detroit, including his All-Pro season in 2017. Now, the two are reunited in Pittsburgh.

"He taught me early at a young age don't use your talent as much," Slay said at his introductory press conference last week. "Only use your God-given (ability) when you need to, and what he means by that is come in the film room, so I kind of learned the game real quick, real early, and people think I'm moving fast as I possibly can but I'm not because I just know they're going probably before they're going. That comes from watching film with T.A. and just trying to make sure I use my ability as long as I possibly can."

Slay is at his best when he's lined up off the ball. That should translate well for the Steelers' predominant Cover 3 scheme as the cornerbacks are most often responsible for the deep outer-thirds of the field. Slay's average depth of target against last season was 12.2 yards. He's more than used to covering receivers downfield.

However, there are two weaknesses that I noticed watching film. First, Slay isn't nearly as lethal when lined up in press man coverage. He doesn't often lose at the release, but his change of direction and reaction time dwindle when he has to run with receivers and stick with them when they break on a route:

Here (top of the screen), Malik Nabers beats with relative ease after breaking off to the outside on the comeback. Slay typically does much better when he plays off-coverage and can read and react instead of trying to match Nabers stride for stride.

The other weakness is, well, the biggest concern everybody has: Slay is slower than he used to be. There's no two ways around that. Even if he's lined up off the ball, a receiver with a lot of speed can still beat him in a footrace downfield:

Even so, that doesn't mean Slay is completely hopeless. While he went the entire regular season without an interception, he did intercept Jordan Love in the Eagles' wild-card win over the Packers -- on a go route, too:

For the Steelers to get the most out of Slay, they need to keep him in off-coverage as often as possible. He's much more effective that way. And not just effective, but still borderline elite in many ways. He may also need some additional safety help over the top to help protect him from getting beat on go routes. That's why signing Juan Thornhill could help out here. He's a centerfielder -- better than Damontae Kazee -- that can let Minkah Fitzpatrick roam free.

Regardless of what concerns you may still have about Slay, the fact is he's still a great coverage cornerback. The actual numbers speak for themselves. According to both Pro Football Focus, Slay ranked third-best in reception percentage when targeted (51.7%) and fourth-best in forced incompletion percentage (20%) among cornerbacks who played at least 350 snaps.

Of course, there's always concern about a cornerback who's approaching his mid-30s. But, Slay's film study habits and instincts make up a lot of the ground lost in losing foot speed over time. That's why his play has yet to drastically decline. No, he's not the All-Pro he used to be, but the Steelers didn't sign him to be that guy. And, they have also committed to him for just one year, so there's minimal risk.

Trying to squeeze every ounce of good football out of Slay, all while he mentors two talented cornerbacks, stands a better chance of being an impactful move rather than a risky one.