When the Cowboys kick off the 2015 season on September 13 against the New York Giants, the Cowboys O-line won't just feature three Pro Bowlers, it may also be the youngest O-line in the league. On opening weekend the following lineup will be a combined 125 years old:

Tyron Smith (24) - La'el Collins (22) - Travis Frederick (24) - Zack Martin (24) - Doug Free (31)



For the Cowboys, the combined age of 125 years may be the most likely but not the only possible scenario. There's also the possibility that Ronald Leary (26) might keep his starting spot over La'el Collins. That would add four years to the total, but the Cowboys would still boast one of the youngest O-lines in the league. There's also the (admittedly remote) possibility that Collins takes over for Doug Free, which would drop the line's combined age to 120.

You can go through any number of iterations along the Cowboys O-line, the result will always leave you with one of the youngest offensive lines in the NFL - and that's quite a turnaround from the offensive line Jason Garrett inherited when he took over as the head coach in 2010. The 2010 starting line of Free (26) - Kosier (31) - Gurode (32) - Davis (32) - Colombo (31) totaled 152 combined years.

A few years earlier, when the Chicago Bears let their offensive line get too old with five starters in their 30s, ESPNs John Clayton came up with what he called the "Theory of 150." Clayton explained that if the combined age of your starting offensive line exceeds 150 years, you should expect a decline in performance.

If a team lets its starting offensive line exceed the total age of 150 years for five starters, the clock is ticking on its remaining success.

Why 150 as a cutoff point? The mathematically inclined may have already figured it out: A combined age of 150 years means the average age of your linemen is 30 years, and as a group, that may be too old. The 30-year age-limit also chimes nicely with the widely held belief that for NFL players, decline inevitably sets in at age 30. Last year, player agent Jack Bechta opined in the National Football Post that teams are more focused on age than ever.

In twenty-even years as an agent I never heard teams talk more about players ages than they do now. If you are on the wrong side of 30, not named Manning, Brady, or Brees, you may as well be ready for a tap on the shoulder any day to be shown the exit.

The graph below shows the age distribution of the 160 projected O-line starters for the 2015 season. The data for the other 31 NFL teams is taken from the Ourlads.com team depth charts, which are usually quite accurate and up-to-date.

What you can see on the chart is that there is indeed a drop among starting offensive linemen in the NFL after 30 years of age. We still have some linemen playing at ages 31 through 33, but there isn't a single projected starter in 2015 who'll be 34 years or older on opening weekend 2015. According to the Ourlads depth charts, the youngest projected starter is the 49ers' rookie center Marcus Martin, who won't turn 22 until November 29, 2015.

But back to Clayton's Theory of 150. Here's how all NFL teams compare in total combined O-line age, based on the Ourlads.com depth charts:

Rank Team Tot. Age Rank Team Tot. Age Rank Team Tot. Age 1 DAL 125 12 KC 132 23 CLE 138 2 JAC 127 13 HOU 133 24 BUF 139 2 MIA 127 13 SD 133 24 WAS 139 4 STL 128 15 PIT 134 26 TB 140 4 TEN 128 16 ARI 135 27 DEN 141 6 ATL 129 16 MIN 135 27 NO 141 6 GB 129 16 NYG 135 29 CHI 142 6 SF 129 19 BAL 137 30 OAK 143 9 CAR 130 19 CIN 137 31 NYJ 150 9 DET 130 19 IND 137 31 PHI 150 11 SEA 131 19 NE 137

Keep in mind that these are averages, and because there are only five guys counting against the total of each team, having an older veteran on the line can give a false impression if you only look at the average.

Looking across the NFC East, notice how the Cowboys have a 25-year lead over the Eagles, a 14-year lead over the Redskins and a 10-year lead over the Giants. The Redskins and Giants have invested first-round picks this year to shore up their aging O-lines, and that has had a positive impact on their O-line age, but Dallas remains far ahead of the curve in this category. What the Eagles are thinking with their geriatric O-line is anybody's guess, but that seems to be par for the course with most decisions out of Philadelphia recently.

For the Cowboys, their investment in the O-line is paying off in more than one way. Not only do they have one of the youngest O-lines, they also have one of the best - and they're getting it at a relative bargain. The five projected Cowboys starters have a cap hit in 2015 of just $12.4 million. The Eagles' five projected starters count $26.6 million against the cap, the Jets' projected starters total $30.3 million against the cap in 2015. And young O-lines also have one more thing in their favor: availability. As O-lines become older, the risk of injury (and with it the risk of missing playing time) increases exponentially.