This season has seen two quarterbacks have historic success for someone over 35 years old.

For Tom Brady, it was not hard to see this success coming. Brady, 36, has statistically been one of the best quarterbacks ever, ranking seventh all time in adjusted net yards per pass (ANY/A), relative to league average.

It is probably not surprising, then, that Brady is having the fifth-best season for a quarterback 36 or older by this metric, with an ANY/A that is two full standard deviations above the mean.

Great as this is, though, Brady does not even lead the league this season among players in this age group.

He is second to Carson Palmer.

Palmer, who is also 36, is second to Peyton Manning (in 2013) in ANY/A for someone over 35, though it was probably harder to see this coming for Palmer.

While Brady has been a top-10 quarterback of all time, Palmer came into the year outside the top-20 in ANY/A+ since being drafted in 2003.

Palmer leads all quarterbacks, of any age, in ANY/A and is second (to Tom Brady) in Passing Net Expected Points (NEP) per pass play this season, and is having a career year despite his age.

His newfound success at his age, and with so much time removed since his last truly great year, make his 2015 a notable one historically.

A Career Year, Out of Nowhere

Palmer has produced 106.07 Passing NEP this season, which indicates how many points above expectation-level he has added with his drop backs. His Passing NEP per drop back of 0.33 is second among the 30 quarterbacks with at least 200 drop backs on the year and is one of only four scores better than 0.23 through Week 10.

As our Barry Cohen wrote a few weeks ago, Palmer’s previous career high in Passing NEP per drop back  was 0.21 in 2005. That season, when Palmer threw for 32 touchdowns and 3,836 yards while averaging 7.1 net yards per pass, was also the only other season in which he eclipsed 100 Passing NEP (113.19).

In the 10 seasons that followed, Palmer averaged just 0.08 Passing NEP per play, with an ANY/A that was only slightly above league average.

Palmer's current Passing NEP per drop back ranks 13th among all quarterbacks with at least 200 drop backs since and including the 2000 season.

The graph below helps indicate how bizarre Palmer’s career arc has been (reminder: ANY/A+ is scaled so 100 is always league average, and 15 points mark 1 standard deviation above or below the mean; this means Palmer’s fluctuation here is not the product of the inflation of passing stats we’ve seen over time).

There is virtually no precedent for a quarterback going so far between excellent seasons.

In 2006, Palmer posted an ANY/A of 6.8, which was just over one standard deviation above the mean. This season is the first year since that has seen him go back above one full standard deviation above average (he posted a 113 ANY/A+ last year, before his season ended due to injury in early November).

Craig Morton is the only other quarterback since the merger to have eight seasons with an ANY/A+ below 115 sandwiched between seasons with an ANY/A+ great than 115.

Morton’s ANY/A in 1971 was exactly one standard deviation above the mean; he did not reach this threshold again until 1981 (he did not play in 1973).

Unlike Morton’s 1981 season, though, Palmer’s 2015 marks the best season of his career and is actually one of the better seasons ever.

In 2005, Palmer’s ANY/A+ was 121, the highest of his career before this season. Through nine games, Palmer’s ANY/A+ is 135.

If he does not throw another pass this season, Palmer’s season would tied for the 22nd best ANY/A+ on record for a quarterback with at least 200 pass attempts in a season (ANY/A dates back to 1969, the first season sack yardage is available).

By looking instead at adjusted yards per attempt (which does not account for sacks), we can look at every quarterback season ever. Here, Palmer ties for 35th best of all time (he has a 133 AY/A+, which is on the same scale at ANY/A+, in that 100 is average and 15 points equal 1 standard deviation).

Palmer’s previous career high in AY/A+ was 2006, when he posted a 119.

He is also in even rarer company in terms of oldest quarterbacks to have a career season.

Since the merger, there have been 287 seasons in which a quarterback has posted an adjusted net yards per attempt average that is 1 standard deviation above the mean.

Of the quarterbacks in this group, Palmer is tied for the third-oldest player to have a career season.

Only Doug Flutie (123 ANY/A+ as a 38-year-old in 2000) and Rich Gannon (126 ANY/A+ as a 37-year-old in 2002) have been older during their career years.

Aside from Palmer, Flutie and Gannon, only 11 other players in this group have had their best seasons in terms of ANY/A+ when they were 35 or older.

It might be hard to explain where Palmer’s career season has come from, but for Cardinals fans, it has surely been easy to enjoy.