Things can change quickly in the NFL. Windows of opportunity seem to slam shut in the blink of an eye. One minute, you're riding high and planning for the playoffs; the next, you're scraping just to win a handful of games.
Several factors make it tough for good teams to stay good, including the salary cap and unrestricted free agency. Technology and the draft, meanwhile, help keep the playing field level by providing a means for bad teams to get better.
As the season approaches, I thought I'd highlight each team facing something like a "now or never" situation in 2013. These are the contenders for whom time seems to be running out -- teams that have a chance to make noise this year, but face serious questions in 2014. These squads had better take advantage of what might be their last, best shot to win for some time, because storm clouds are gathering. Teams are arranged according to the likelihood that hard times will come in 2014.
1) Pittsburgh Steelers
The Steelers' defense is getting older. The important trio of cornerback Ike Taylor (33 years old), safety Troy Polamalu (32) and linebacker LaMarr Woodley (28) is coming off a season in which each guy missed significant time. Of course, that didn't stop Pittsburgh from ranking first in total defense and sixth in scoring D, but it will be very difficult to maintain that performance level with such an old core. In March, meanwhile, Ben Roethlisberger turned 31, the age at which most quarterbacks hit the wall and begin to regress, especially when it comes to key metrics like completion percentage, interceptions and touchdown passes.
I think Pittsburgh is good enough to contend in 2013, but things promise to get more difficult in 2014, especially considering the competition in the AFC North. The Baltimore Ravens and Cincinnati Bengals are both set with promising young quarterbacks in Joe Flacco and Andy Dalton, respectively, meaning they'll likely be even tougher to beat a season from now.
2) New York Giants
It's hard to believe Eli Manning is 32 years old, but it's true; he's one year past the age at which quarterbacks generally begin to lose effectiveness. Now, Manning's career trajectory won't necessarily follow that rule, given that he's managed to escape serious injury thus far -- healthier guys typically hit the wall later than oft-injured players -- but his age is still worth considering. Manning, of course, isn't the only member of the Giants getting up there in age; the defense is also older. How much longer will Justin Tuck (30), Mathias Kiwanuka (30) and Corey Webster (31) be able to play at a high level? Meanwhile, Chris Snee, the leader of the offensive line, is 31, while guard Kevin Boothe is 30. And New York has bare-bones depth at tight end; position coach Mike Pope needs to pull a rabbit out of his hat.
This franchise is extremely well-run, and the Giants usually find a way to get over the hump, but New York has important issues to consider in the near future. Looking ahead, the division race only figures to get more competitive as the Robert Griffin III-led Washington Redskins continue to establish themselves as contenders.
3) Chicago Bears
New defensive coordinator Mel Tucker will squeeze everything he can out of an aging defense that really has just one established young star in Henry Melton (26). Key defenders Julius Peppers (33), Charles Tillman (32) and Lance Briggs (32) are all over 30, while Tim Jennings will turn 30 in December. Offensively, the Bears figure to face plenty of questions in 2014, when receiver Brandon Marshall will turn 30 and quarterback Jay Cutler can become a free agent.
The NFC North, meanwhile, doesn't look like it will get much friendlier in the next few years. Still, forward-thinking general manager Phil Emery is a big plus for the Bears franchise.
4) New England Patriots
The Patriots face questions beyond their much-publicized issues at tight end. How much longer can Tom Brady, who will turn 36 in August, continue to play at a high level? New England's best defensive player, Vince Wilfork, will turn 32 in November. Bill Belichick is one of the best coaches ever, and he'll be able to shepherd this team through this season, but the 61-year-old is entering his 14th season at the helm in New England -- one year past what Al Davis considered to be the shelf life for an NFL coach. New England has dominated the AFC East in the Belichick era, but that should be a bit tougher to do in 2014, given the improvements being made by the Miami Dolphins and Buffalo Bills.
5) Denver Broncos
The Broncos look to be in good shape for 2013, thanks to the additions of free agent receiver Wes Welker and rookie running back Montee Ball, but the age of quarterback Peyton Manning makes the future a bit murkier beyond that. By 2014, Manning will be 38 and starting his 17th year in the league. You have to wonder how long he can continue to excel. If Manning needs relief this year or next, who will the Broncos turn to? Current backup Brock Osweiler has raw talent, but lacks experience; I don't see a young quarterback on their roster who can step in and play well. Manning is still thriving, but think of Johnny Unitas and how he eventually fell off after leaving the Baltimore Colts for the San Diego Chargers at age 40.
On the defensive side of the ball, cornerback Champ Bailey is 35, while coordinator Jack Del Rio has to find someone to replace departed defensive end Elvis Dumervil, so that opposing offenses can't solely focus on outstanding pass rusher Von Miller.
6) Houston Texans
The Texans have an above-average chance of winning the AFC South and look like Super Bowl contenders in a wide-open conference race. They have a very good defense led by 24-year-old J.J. Watt, whom many think is the best defensive player in the NFL. They also have good, young running backs in Arian Foster (26) and Ben Tate (24), and a promising rookie receiver in DeAndre Hopkins.
But that doesn't change the fact that two of Houston's most important offensive players -- quarterback Matt Schaub and receiver Andre Johnson -- will both be 33 by the time the 2014 season rolls around. In the meantime, the rest of the division will only improve, which means that this might be the Texans' last chance to make a meaningful playoff push for some time.
Follow Gil Brandt on Twitter @Gil_Brandt.