On Sunday night, the Colts’ Marvin Harrison caught Peyton Manning’s only touchdown pass during Indianapolis’s big 20-10 victory over AFC rival Baltimore. As Manning’s favorite target for the better part of the last decade – the tandem owns the record for most receptions by a quarterback receiver combination – Harrison has been a primary beneficiary of Manning’s chase for Dan Marino’s single season record of 48 touchdown tosses.

Harrison and Manning have been so prolific over the years that, with Manning signed through 2010, the Colts signed Harrison two weeks ago to a seven-year, $67 million contract extension, including $23 million in guaranteed money. It was the largest total contract ever signed by a wide receiver, a worthy reward for a player who has been an instrumental part of the most potent offense in football and is seventh all-time in receiving touchdowns.

But good teams sign contracts based on future performance, not past performance. At the age of 32, will Harrison have enough good years left to provide value commensurate with his paycheck? The answer to that question now seems more likely to be “yes” than we might have thought a year ago.

Four years ago, statistician Doug Drinen produced a study pinpointing the peak ages for the NFL’s offensive skill players. He found that running backs generally begin to decline after the age of 28, quarterbacks after the age of 32, and wide receivers after the age of 30.

At age 32, Harrison should be in his decline phase, and indeed his yardage totals have dropped each of the past two seasons. But Harrison’s reduced output results more from Indianapolis’s ability to spread the ball around on offense than from any decline in his individual skills. More importantly, the performance of several other aging receivers this season gives reason to believe that 30 should no longer be considered the cutoff age for wide receivers.

Three of the NFL’s top five receivers in total yardage this season were drafted in 1996, the same year as Harrison. Joe Horn of New Orleans, who leads the league in receiving, is 32 years old. Philadelphia’s Terrell Owens and Carolina’s Mushin Muhammad are both 31.Jacksonville’s Jimmy Smith,35,and St. Louis’s Isaac Bruce, 32, are also in the top 10. By comparison, last year’s list of the top 10 receivers had only two players over the age of 30, and 2002’s list had none.

Last year, as they began to enter their 30s, nearly all the receivers from the class of 1996 saw their total yardage drop. This year, these veteran wideouts aren’t just managing to stave off decline; a number of them are having seasons that match the best of their careers.

Horn, for example, had only 973 yards receiving last season; this season he already has 1,248 yards receiving and is less than 100 yards away from setting a new career high. Muhammad, elevated back to the top receiver position after an early-season injury to Steve Smith, currently has 1,195 yards after hauling in fewer than 850 in each of the past three seasons.

Other receivers who have already passed their yardage totals from last season by at least 100 yards include Jacksonville’s Jimmy Smith; Denver’s Rod Smith, 34; Buffalo’s Eric Moulds 31; and Dallas’s Keyshawn Johnson, 32. And the big years are not only due to more catches and more opportunities; most of these receivers have increased in yards per catch as well as the number of catches.

To discover a major reason behind this sudden surge from players who should be in decline, we have to look back at the last season when the effects of age suddenly reversed themselves among the league’s top receivers: 1994. That season, four of the top 10 receivers were over the age of 30, including 30-year-old Andre Reed, who jumped from 854 yards to 1,303 yards, and 33-year old Henry Ellard, who went from 945 yards to 1,397 yards.

What 1994 and 2004 have in common is the renewed emphasis on illegal contact penalties. Ten years ago, in an attempt to open up the passing game a bit, the NFL added the so-called “chuck” rule, which prohibited contact more than 5 yards past the line of scrimmage. The beneficiaries of this rule change included many older receivers who suddenly reversed their decline.

Over the next 10 seasons, referees gradually called this penalty less and less. So this season, the NFL competition committee clarified the language of the rule and instructed referees to emphasize it once again. And the effects have been the same as 1994 – including the big years from wide receivers in their 30s.

Why should a change in the way penalties are called effect older receivers more than younger ones? It’s often stated that there is holding on every NFL play, and the same goes for other penalties. For every play where illegal contact is called, there are a number of plays where the referees miss the violation. An experienced veteran knows how to draw the call, and how to take advantage of the freedom created when defensive players, fearing a call, play slightly more passive coverage.

As players get older, their bodies slowly break down, and they depend more on veteran guile. A player’s peak comes when he can combine the athletic ability of youth with a few years worth of experience. By enforcing the illegal contact penalty, the league has made veteran guile more important, which allows players whose bodies are beginning to decline to remain among the NFL’s best.

It will take another year or two to determine if the peak age for wide receivers truly has shifted and become slightly older. In signing Harrison to such a large contract, the Colts are counting on the continued enforcement of illegal contract rules, which will help Harrison play at a high level longer into his career.

Maybe Harrison can even play as long as the 32-year-old receiver who led the NFL in receiving the first time the illegal contact rule was put into place, and is still in the league today: Jerry Rice.

Mr. Schatz is the editor in chief of FootballOutsiders.com.