The law of averages says some pretty mean things about players of a certain age.

It says NFL running backs who reach the age of 30 start to experience a precipitous decline. It also says that age 40 is a magic number in baseball. Once you hit that mark, if you’re lucky enough to get there, not too many good things are going to happen the rest of the way.

Alex Rodriguez has spent much of this season pointing out that within the law of averages there is also the flaw of averages.

A-Rod, who smacked three home runs Saturday in a season-defining 8-5 Yankees win over the Twins (until, at least, another season-defining game next week), turns 40 on Monday. He has spent much of his time since 2011 trying to come back from injury, embroiled in controversy or both.

This season, which began with obvious questions about how much Rodriguez still had left after missing all of 2014, has turned into a comeback story almost as stunning as the comeback at Target Field on Saturday.

While it’s possible now that Rodriguez is officially at that magic 40 number, he suddenly will forget how to swing a bat and never hit another home run, those vicious cuts he had Saturday suggest otherwise. They suggest that while he is certainly just a percentage of the great player he was (drugs or no drugs) in his prime, we can never say for sure when an elite player is cooked.

And as disheartening as it was for Twins fans — many of whom booed him lustily Friday and Saturday before he took a day off Sunday — to watch A-Rod bash his way around Target Field, those who also root for the Vikings can take heart in the lessons he offered as they pertain to a certain running back.

Adrian Peterson, too, has spent much of his time since 2011 trying to come back from injury, embroiled in controversy, or both. He had the best season of his life in 2012, of course, but 2013 was a significant drop-off (from 6.0 yards per carry to 4.5) and we all know what happened in 2014. Now Peterson is 30, and conventional wisdom is to wonder how much he has left in the tank.

The law of averages says he will be just a little bit slower, a little less resilient and that we will start to see a decline. Peterson eschews such talk and boasts of setting his sights (again) on 2,500 yards rushing this season.

The law of averages says that’s pretty much impossible. The flaw of averages is that it works toward the middle instead of the extremes. A-Rod is an extreme. And Peterson has shown in the past that he is, too.