This rumorhas been around for a while, but ESPN reported more details Sunday about the Calvin Johnson retirement saga, citing sources who suggest Johnson is “content” with his decision to call it quits. Johnson may have his reasons — health-related or otherwise — to retire, and he can do what he pleases. (I, for one, enjoy seeing players come and go for thesheer information value of it all.) But whatever is going on, it should be clear this isn’t a matter of Megatron’s career having run its natural course.

Johnson, who won’t turn 31 until September, would be one of the most shocking retirements since fellow Detroit legend Barry Sanders bowed out of the league after the 1998 season. But Sanders – also 30 at the time and considered by some to be in his prime – had just matched the lowest yards per attempt of his career for a 5-11 team. And more importantly, he was a running back. Running backs don’t age nearly as well as receivers.

Since the 1970 merger, there have been294 seasons of 1,200-plus rushing yards and just 24 of them came from running backs aged 30 or older. Meanwhile, there have been258 seasons of 1,200-plus receiving yards, with 56 by players aged 30 or older. While most starting receivers are usually in their mid-to-late 20s, we do start seeing significant attrition around the 30-year mark. It isn’t surprising that non-productive older receivers are quickly replaced by younger, cheaper alternatives. But for those with the skill and good fortune to stick around, there isn’t any drop-off in average performance.

Here’s how Johnson compares to the gaggle of receivers who started the majority of a season since 1970 ^{26 1} :

And though 2015 certainly wasn’t the best year of Johnson’s career, he hasn’t shown any unusual swings in his production — even the “cliff” after his record-setting 1,964 yards in 2012 is consistent with regression to the mean (not to mention he missed several games yet scored far more touchdowns) — and is still well above average.

Retirements by receivers still producing at a level as high as Johnson are almost nonexistent. The closest example is probably Packers receiver Sterling Sharpe, who had to retire after a severe neck injury at age 29. Sharpefinished his career with 8,134 receiving yards and 65 receiving touchdowns, whileJohnson has 11,619 receiving yards and 83 receiving touchdowns. Johnson’s total is actually the second-most yards by a receiverby age 30 since the merger, and most of the other top receivers on that list still had thousands of yards ahead of them:

Further, Johnson’s 1,214 yards this season are the 14th-most for a 30-year-old since the merger. Production as a 30-year-old is a pretty good predictor of future career success for receivers, and it also suggests that Johnson might have 4,000-plus yards left in him:

Of course, both of these curves are skewed by Jerry Rice. Moreover, Johnson has had to shoulder a heavy burden in his career. So, I experimented with a number of variables to predict production among NFL players in their late 20s and beyond (call it back-of-the-envelope modeling). I found that — in addition to age — the most recent season is the most significant predictor, but that both past performance and burden are statistically meaningful as well. ^{27 2}

With all of this taken into account, the balance of Johnson’s career projects to be the fifth-most productive among those of active NFL receivers age 25 and older:

(Note that combining Johnson’s current receiving yards with his projections would put him ahead of Terrell Owens for second on the all-time yards list behind Rice, though Larry Fitzgerald and Brandon Marshall both project even higher totals than Johnson.)

If Johnson ultimately decides to leave, good for him. If he ultimately decides to stay, good for football.