Being only 25 years old, the best athletes I've ever seen are -- for the most part -- still playing professionally.

Sure, there are plenty of players who have retired in the past 10 years or so, guys I saw a lot of. But in terms of players I saw from the start of their careers to the end? That's still a new feeling for me.

So when superstar wide receiver Calvin Johnson told his team, the Detroit Lions, that he planned to retire this offseason, I felt an array of emotions.

Now, I'm not a super big Megatron fan, and in a weird way, knowing he still has something to contribute makes me feel younger, but dang, Johnson is still operating at the peak of the NFL.

Hopefully the Lions can figure out a way to bring him back for next season -- because, as you'll see, Megatron is still bringing the heat -- but if this really is it, we need to appreciate Johnson for the longstanding success he's had (in spite of quarterback woes and other shortcomings).

Calvin's Career

You can gauge Johnson's career (to date) in any way you'd like. You can cite his six Pro Bowls, his three first team All-Pro selections, his two seasons leading the league in receiving yards and touchdowns, his single-season record for receiving yards, or whatever else you want.

Those are great, but they don't indicate just how big an impact he had on his team throughout his career. And if you, like Hall of Fame receiver Lynn Swann, don't think Johnson has done enough to make his team great, well, you're wrong.

That's not just my opinion. That's what's true based on our Antonio Brown (419.33) and Demaryius Thomas (378.35) are well above him, but both topped 300 catches (375 for Brown and 308 for Thomas) while Johnson reeled in 243, and both topped 500 targets (541 for Brown and 503 for Thomas).

You might want to argue that his lack of receptions has a lot to do with his catch rate, which might make some sense. His 56.1 percent catch rate ranked a lowly 93rd in this group of 125 receivers and tight ends.

Wasted chances, yeah?

Well, maybe. In the past three seasons, per SportingCharts, Johnson has dropped 15 of 434 targets (a 3.46 percent drop rate). For context, that would have been the 13th-highest rate among the 42 players with at least 100 targets this year, but his mark has been below 3 percent in the past two years.

Surely these unproductive targets have diminished his overall efficiency, but stick with me.

Of his 243 catches in the past three seasons, 230 of them have actually added to Detroit's expected point total. That's a Success Rate of 94.65 percent, one that ranks second among the 125-player subset.

Only one other player in the top 18 in targets in that span has a mark above even 90 percent (DeAndre Hopkins, 90.79 percent). You have to go the whole way down to Vincent Jackson (93.92 percent and 19th in targets) to see someone come close to his success with actual catches.

In fact, among the 26 players with at least 200 catches in this span, Johnson's 1.46 Reception NEP per reception is about as far from second place Alshon Jeffery's 1.30 as Jeffery is from 10th place Anquan Boldin (1.15).

Even if you factor in the drops and wasted targets, Johnson has been so good on a per-catch basis in the past three seasons that his Reception NEP per target (0.82) is tops in that 26-player group -- despite ranking last in catch rate (56.1 percent).

Greatness Defined

Say what you will about the low catch rate and even the drop rate if you want, but playing receiver in the NFL depends on more than individual talent.

Quarterback Matthew Stafford hasn't really been a top-10 talent in the league, based on our metrics, and he finished 16th in Passing NEP this year (behind Jay Cutler, for what that's worth). That's not an excuse for anything, but it is the truth. Johnson has been unmatched when he catches the ball and has been so good on receptions that he stands up to his peers on a per-target basis.

No, the Detroit Lions haven't been flooded with Super Bowl rings because of Calvin Johnson's performance, but it's hard to say that any receiver -- regardless of team situation or success -- has impacted his team quite like he has since 2007.

And perhaps more important is that even after his record-breaking 2012 campaign -- a stint marred by injury, waning raw stats, and the onset of the next generation of elite receivers -- Johnson has been as good as ever.

And that -- by many measures -- makes him one of the NFL's best receivers even as he contemplates hanging up his cleats for good.