Bob Stoops was a very good football coach for a very long time. It's easy to take head coaches like Stoops for granted. Stoops went 13-0 and won a National Championship in his second year on the job. He never won another, but there are now only four active head coaches in college football who have won a national championship: Urban Meyer, Nick Saban, Dabo Swinney and Jimbo Fisher. Stoops' replacement will be taking over a program that went 190-48 in 18 seasons and is coming off yet another first-place finish in the Big 12. That replacement was already on the staff, Lincoln Riley, and he was 17-years-old when Oklahoma won their last national championship, and that worries me.

Age may just be a number, but it matters when forecasting how a head coach will fare long-term. Saban was in his early fifties when he first won a National Championship at LSU. Meyer, Fisher and Swinney were all in their late forties when they first won the big one. The list doesn't stop there, as you can look at when Mack Brown (54) finally won at Texas, when Phillip Fulmer (48) won at Tennessee, and the list goes and on from there.

Riley won't turn 48 — the ostensible sweet spot for coaches to win their first national title — for fifteen years.

But that's not to say Riley can't be a fine stop-gap head coach in Norman, because he can and probably will be. Like some of the coaches on this prestigious list — Fisher and Fulmer, specifically — they, too, were promoted from offensive coordinator to head coach and ended up winning national titles for their universities.

But they were older and more experienced.

Riley is a gifted offensive mind who has put together an offense at Oklahoma that just works. Last season, the Sooners were No. 3 in the nation in points per game (43.6). With veteran quarterback Baker Mayfield returning for what seems to be his seventeenth collegiate season, the Sooners' offense will likely continue to roll over the competition once again in 2017. The team lost several major weapons on offense — Joe Mixon, Dede Westbrook, and Samaje Perine — but they also just reeled in the eighth-best recruiting class in 2017.

With Stoops or Riley at the helm for the 2017 season the Sooners were always going to win a lot of football games. They were going to have a real Heisman contender under center, a top-10 offense and a defense that was above league-average in points allowed per game at 28.85. Everything would have looked the same except for who was roaming the sidelines: Stoops in Year 19 on the sidelines in Oklahoma or Riley in Year 1 on the sidelines in Oklahoma. The former has the feel of a potential National Title run, and the latter has the feel of a rebuild.

Riley may indeed turn out to be the right long-term answer for the Sooners, but this is not a program that needed to rebuild and regroup — like their rival in Austin with Tom Herman. Rather than promote the young, rising head-coaching candidate in Riley, the Sooners could, and, really, should have looked elsewhere.

And they should have.

Had the Oklahoma job become officially open, it's fair to assume the job would have generated a lot of interest from big-time, veteran coaches who are win-now mode. Coaches in the age range that has won national championships.

Here are three coaches who would have made a lot of sense for Oklahoma.

Dan Mullen, Mississippi State

Mullen, 45, is already the best coach in Mississippi State's history. Like Stoops in the late '90s, Mullen worked under a coaching legend at Florida before landing his first major job. And he's found a way to build a consistent winner in Starkville, MS. There may not be a more underrated head coach in college football, and, with the right defensive coordinator, Mullen and the Sooners could have been the perfect fit.

Chip Kelly, Free Agent

Kelly, 53, has already won at the college level, and, although his NFL career didn't go the way he would have liked, he knows how to run an effective collegiate offense. We know he can recruit at a high level, and with Mayfield and quarterback-in-waiting Kyler Murray on the roster, Kelly is one of the few coaches who would be able to step in immediately and keep their offense rolling.

Brian Kelly, Notre Dame

The Other Kelly, 55, and perhaps the bigger long shot, doesn't seem likely to be in South Bend, IN. for the long haul. Coming off a 4-8 season, Kelly may not be the sexiest hire to replace someone like Stoops, but Kelly recruits at the same, top-10 level as the Sooners. His career record, though, still sits at a very impressive 230-88-2. Kelly has shown he can win anywhere.

It's easy to see why the Sooners went the safe route with Riley. Why rock the boat? Riley's offense has proven to be a huge asset for the team, and, had they went with an outside hire, they probably would have lost him. It was going to be tough decision regardless, and, although Riley may continue the tradition of winning 8-plus games for years, it still feels the riskier play and one that Oklahoma fans should worry about.