Peyton Manning’s short free agency prompted a healthy debate about the merits of putting the fortunes of your franchise in the hands of a 36-year-old quarterback coming off a neck injury serious enough to require multiple surgeries and sideline him for an entire season.

Skeptics cited Johnny Unitas and Joe Namath as examples of once-great quarterbacks who tried and failed to rekindle past glory with new teams late in their careers. But then, Unitas was 40 when he played his final, forgettable season in San Diego after 17 years in Baltimore, and Namath could barely walk by the time he played an equally cringe-worthy final season for the Rams after 12 years with the Jets.

(By the way, these two greats put on what some consider the best passing exhibition in NFL history on Sept. 24, 1972 in Baltimore, where they combined for 872 passing yards. Namath threw for 496 yards and six touchdowns in a 44-34 win, the Jets’ first victory over the Colts since Super Bowl III almost four years before. Unitas threw for 376 and three touchdowns.)

On the other hand, although John Elway never changed teams, he did achieve his greatest success very late in the day, winning his two Super Bowls with the Broncos at ages 37 and 38.

The best example of a quarterback changing teams and achieving success late in his career is Jim Plunkett, like Elway a Stanford star and first overall pick in the draft. Plunkett struggled in his early stops at New England and San Francisco. He joined the Raiders in 1979, the year he turned 32. A year later, at 33, he led them to the first of his two Super Bowl championships. He threw for 261 yards and three touchdowns and was named most valuable player as the Raiders became the first wild-card team to win a title, beating the Eagles 27-10. Three years later, at 36, he led them to his second, a 38-9 romp over the Redskins.

“It’s about the all-around personnel,” Plunkett explained recently during an appearance on the Dave Logan Show. “You’re playing with a better group of people. You’re playing with a team that has a defense. You’re not always playing catch-up all the time. A team that’s used to winning. That’s a big plus as well. They expect to win each and every game every time they step on the field.

“It was a struggle initially for me both at New England and San Francisco. I wanted it to work out in the worst possible way for me back in my home area and it just did not. I joined the Raiders and I’m playing with a lot of Hall of Famers-to-be, guys who are used to winning, guys who have a winning past. They just surround you with more better players to get the job done.”

I mentioned Unitas and Namath and asked Plunkett what the primary differences are between older quarterbacks who save their best for last and those clearly on the downhill side of their careers.

“Part of it has to do with health,” he said. “Part of it has to do with the team you’re around. As you get older, you get hurt more. I just found that to be my case after that second Super Bowl, and even a little bit before. It was hard for me to stay healthy. I’d get nicked up a little easier. Of course, part of it was my style of play. Instead of going down like I should, I’d hang in there and get my head knocked off and in the process got beat up quite a bit.

“Peyton Manning’s had a lot of luck in that regard up until lately. And it still remains to be seen how well he bounces back. One of the things everybody’s hoping, especially the Broncos, is that he hardly misses a beat and he comes back strong. But then you’ve got to still surround him with the type of people and run the kind of offense that he’s used to, I think. That would be a big plus for him. The personnel’s just different. It was geared (in Indianapolis) to make Peyton Manning a better quarterback on offense. Right now, they might not have those kind of people at Denver in place yet.”

Plunkett, who continues to cover the game as a radio and television host for the Raiders, offered this overall assessment of Manning as a quarterback and his prospects moving to Denver:

“I see a guy who gets rid of the ball quickly, who reads defenses quickly, throws prior to the break. I’ve seen him a lot. I saw him in that great championship game when they were down 21-3, I believe, to the Patriots at halftime (the 2006 season AFC championship on Jan. 21, 2007, in which the Patriots led 21-6 at the half and the Colts came back to win, 38-34). To watch him bring that team back against a very good football team was quite impressive. The Patriots were able to put a lot of pressure on him, but the guy’s just got a great ability to anticipate where that receiver’s going to be and get rid of the ball, even though the protection’s not that good. Hopefully, that’s the kind of quarterback that Denver’s going to get.

“But also you’ve seen guys with injuries, and I’ve seen it a lot with broken jaws for some players, especially linebackers and running backs. Those guys that have broken their jaw, for whatever reason, when they come back, they’re kind of tentative. They’re afraid to put their head in there because it hurts. It’s something you’ve got to overcome. I had a few knee operations when I was playing and after you get your first hit and you get knocked down, you’re kind of testing out your knee to see if it’s OK. And I think Peyton might have to go through some of that when he comes back and starts to get hit and knocked around: ‘Is my neck going to hold up?’ And he might be kind of tentative until he takes a few shots and sees how sturdy or not that his neck is.”

Immediately after signing Manning, Elway moved to improve the quality of the weapons around him. He added wide receiver Andre Caldwell to incumbents Demaryius Thomas and Eric Decker. He also signed a pair of receiving tight ends in Joel Dreessen and Jacob Tamme, the latter a teammate of Manning’s with the Colts.

Plunkett put his finger on the two key ingredients if the Broncos are going to enjoy the kind of success with Manning that Elway is banking on:

1. Manning must stay healthy, fully recovered from his neck injury and not suffering other, nagging injuries that often contribute to the deterioration of play in older quarterbacks.

2. Elway must surround him with the right personnel. If anyone understands this, Elway should. After three Super Bowl losses, it was the arrival of Terrell Davis that finally gave him the opportunity to win championships. Manning may not need a 2,000-yard rusher, but Elway will have to get the supporting cast right for the $96 million gamble on a 36-year-old Hall of Famer-to-be to succeed.

The Broncos ranked 23rd in total offense and 25th in scoring offense last season. Some of that, obviously, was the result of a run-dominated scheme built around the skill set of quarterback Tim Tebow. The Broncos ranked first in rushing, at 165 yards a game, and 31st in passing, at 152. Those numbers are likely to change quite dramatically with Manning at the controls.

Somewhere along the way, Manning will have to find the sort of working relationship with Broncos receivers that he enjoyed with Marvin Harrison, Reggie Wayne and Dallas Clark for him to replicate the success in the passing game he achieved in Indianapolis.

Do the Broncos have receivers capable of that on the roster currently? We’ll soon find out.