Back in March, Chase wrote a post investigating how quarterbacks age , finding that they peak at age 29 (with a generalized peak from 26-30) in terms of value over average . Today, I thought I’d quickly look at how quarterbacks age in terms of their performance rate — specifically, their Adjusted Net Yards per Attempt (ANY/A). For newer readers, ANY/A is based on the following formula: (Passing Yards + 20 * Passing TDs – 45 * INTs – Sack Yards Lost) / (Pass Attempts + Sacks).

First, I need to introduce a way of adjusting ANY/A for era: Relative ANY/A. Relative ANY/A is simply equal to:

QB_ANY/A – LgAvg_ANY/A

The table below lists the 30 single-season leaders in Relative ANY/A since the merger. You won’t be too surprised to see the 2004 version of Peyton Manning at the top. That year, Manning averaged 9.8 ANY/A, while the league average was just 5.6 ANY/A. That means Manning gets a Relative ANY/A grade of +4.1 (with the difference due to rounding).



Using this, we can evaluate every quarterback’s season independently of era, and compute the year-to-year differences in Relative ANY/A at every age.

Taking every quarterback who had at least 15.1 dropbacks per game (which tends to correspond to the standard 14 attempts per team game) in back to back seasons, I fed the year-to-year Relative ANY/A deltas into a cubic regression and smoothed out an aging curve. (This is the same process I used to calculate an aging curve for basketball players for ESPN Insider last year.)

According to this methodology, here’s how a QB can expect his Relative ANY/A to change from year to year at each age:

From Age To Age Delta 20 21 +0.88 21 22 +0.66 22 23 +0.47 23 24 +0.32 24 25 +0.20 25 26 +0.10 26 27 +0.02 27 28 -0.04 28 29 -0.08 29 30 -0.11 30 31 -0.14 31 32 -0.15 32 33 -0.17 33 34 -0.19 34 35 -0.21 35 36 -0.24 36 37 -0.28 37 38 -0.33 38 39 -0.40 39 40 -0.50 40 41 -0.61 41 42 -0.76

Or in graphic form:

This would indicate that on average, quarterbacks peaks at age 27. To put the data in another light, if we created a passer who peaked at 8.0 ANY/A, and he perfectly followed this age curve, here is how his ANY/A would look each season:

One big caveat with this study: there’s probably a good deal of selection bias here, in the sense that only passers deemed to be good enough to keep playing will get a chance to put up 15.1 dropbacks/game the following year. Still, I think this provides a pretty good estimate of how much improvement/decline you can expect from a guy at a given age.

Armed with this aging curve, we can do a lot of cool things in subsequent posts, so stay tuned….