Naturally, I had to research where that calculation came from. There are actually lots of sophisticated attempts to calculate heart health and "fitness age" with equations that are based on study-derived data.
The one for his P.E. class came from an outfit called FitnessGram that provides health-measurement approaches for P.E. classes. That's all I'm going to say about FitnessGram because I don't have time to research it, but here's the equation for maximal oxygen capacity or VO2 max (basically, how strong and efficient your lungs and overall cardiovascular system is):
.21(age) – .84(BMI) – 8.41(run min) + .34(run min2) + 108.94
The inputs include age, body mass index (BMI), and how fast you can run a mile in. Here's a BMI calculator; there are many of them on the web. Whenever a fitness equation includes numerical anomalies like ("take everything and add 108.94…") I wonder about their accuracy.
I pumped in my numbers, assuming I can run a mile in 7:12. (I can go faster than that, or slower, I just haven't run a mile lately and am guessing). The result I got was 58.6, which seemed high for me right now.
Another "fitness age" calculator comes from a well-reported study out of Norway.
This calculator takes different parameters, including how hard you train, how often you train, your age, your waistline, and your resting pulse rate.
It is based on a study conducted with thousands of Norwegians between the ages of 20 and 90. It found a very high correlation with VO2 max and metabolic health or disease (the lower the VO2 max, the more likely the person had or was headed for the metabolic syndrome.)
The Norway calculator gives you an estimated VO2 max and a "fitness age." The VO2 max estimate for me was 53; probably much closer to the truth than 58. But this shows how the estimates can differ widely for the different calculators, despite the reams of data they have used to build their equations.
For comparison sakes, Bjørn Dæhlie the great norwegian nordic ski racer had a VO2 max in the 90s, and Greg LeMond the U.S. Tour De France cyclist had one that was around 92, and the great late runner Steve "Pre" Prefontaine clocked in at 84.
All the calculators assume that higher VO2 max and low heart rate is always better, and I'd like to see more sophisticated assumptions built into them that take into account the damage you can do with excessive training, and driving your heart rate down to absurdly low levels, like 35 bpm.