This is a breakdown (by age) of the 338 players in NFL history who had the best single seasons, as determined using @pfref ‘s seasonal AV stats.  Here is a link to the data used in this study.

age number of players
21 2
22 11
23 20
24 44
25 37
26 46
27 41
28 27
29 27
30 22
31 15
32 16
33 14
34 8
35 3
36 2
37 3

The AV stat from is a number they give to each player each season, the higher the better.  AV stands for approximate value, and provides us with a way to compare players at different positions (e.g. offensive guard versus cornerback) with one another in order to determine which player had the better season.  These are objective numbers based on stats, and also take into account post season honors, such as pro bowl, first team all pro, etc.

The top season any player has ever had, according to this metric, is LaDainian Tomlinson’s 2006 season in which he scored a 26 AV.  In 2016, the MVP of the league was Matt Ryan, who had a 21 AV that season.  The lowest graded player seasons (among these top 338 seasons ever) had 18 AV.  Just to put things into perspective, Saints rookie receiver Michael Thomas scored a 10 AV for his rookie season.  The Saints players who made this list were Jahri Evans (twice), Carl Nicks, Pat Swilling (twice), Sam Mills, and Drew Brees (20 AV for the 2011 season).

The age group with the most representatives in this list was 26.  There were 46 26-year-olds in the list, 44 24-year-olds, and 41 27-year-olds.  Ages 24-27, inclusive, are clearly the prime years for NFL players.  This should come as no surprise to anyone.  So, when does Father Time really start catching up with players?  28 is the first dropoff, but then 30, 31, and a big dropoff at 34, and another big one at 35.  I believe the reason we don’t have more younger players (23 and under) represented is simply because there aren’t as many of those younger players in the league.  Most would still be playing college ball at 21 or 22, and then inexperience would be a disadvantage for most 23-year-olds.

These are the players that made the list at 34+ years-of-age:

Tom Brady 34
Rich Gannon 34
Johnny Unitas+ 34
Steve Beuerlein 34
Reggie White+ 34
Kevin Greene+ 34
Night Train Lane+ 34
Joe Theismann 34
Randall Cunningham 35
Doug Wilkerson 35
Tom Brady 35
Steve Young+ 36
Rich Gannon 36
Peyton Manning 37
Sam Mills 37
John Elway+ 37

As you can see, the quarterback position is well-represented with these older players.  Quarterbacks don’t need the athleticism that comes with youth as much as other position groups, relying instead upon their experience and cunning to get the job done.  Interestingly, if you sort by top AV numbers, the top 3 spots are all running backs, ages 26, 27, and 28 (LaDainian Tomlinson, OJ Simpson, and Marshall Faulk).

Conclusion?  Well, if you’re looking for a free agent to bring in and save the season, try to find one in that 24-27 age range as these are the ones most likely to have a great season for you, unless it’s a quarterback where age is less important.  Teams should probably pass on 31+ year old running backs.  (I’m just saying…)