I'm not watching a lot of the Olympics (I prefer the winter events), but the performances I've seen have been pretty impressive. And as I get older, I'm more amazed at how young some of the athletes are, and how short their careers end up being. There are many older Olympians, but the most athletically-demanding competitions favor youth.

It's not so different in professional football. Youth is important, with some older performers still in the game. So in fantasy football, I often find myself considering the opposing forces of nostalgia and ageism. If you're not careful, one or the other could hurt your draft.

On one hand, there's plenty of youth at the front of most cheat sheets. Second-year player Todd Gurley is usually near the top, and rookie Ezekiel Elliott isn't far behind. On the other hand, Adrian Peterson is in the top tier of most lists as well.

Elliott is more than a decade younger than Peterson. That's like three average NFL running back careers in between them, and AP is still playing. Can we feel good about taking a guy that old? I know he heals faster than most humans, and he had a lost season (which saved wear and tear). And he put up great numbers last season. Still, he's 31. That means something.

But you know who else is 31? Michael Phelps. He should have retired years ago, but he's still winning gold against the best in the world. He even stares down his rivals. I'm watching him do things he shouldn't be able to do at that age, and it makes me think of Peterson. Some athletes are different, and they shouldn't judged by a normal standard.

At quarterback, it's assumed that Tom Brady will have something to prove when he comes back from suspension. The Patriots play best with a chip on their collective shoulder, and their opponents are usually the ones who suffer. Combined with a penchant for running up the score (or at least not being too sorry if it happens), you have to consider Brady a player worth drafting. Same with Drew Brees, who put up close to 5000 yards last season while he's "in decline."

Still, Brady is 39, and Brees is 37. For quarterbacks (even Hall of Fame-bound quarterbacks), that's old. It's the age of a game manager, not a gunslinger. At that age, it's hard to compete at the highest level.

But shouldn't the same be said for Venus and Serena Williams? At 34 and 36 -- which is beyond ancient in tennis -- they just made headlines for losing at the Olympics for the first time in their doubles career. While they've both been eliminated from singles competition as well, it's amazing that they competed in Rio. History suggests they should be in the broadcast booth by now. Instead, they're both ranked in the top 10 today (Serena's been the top-ranked player for more than three years) and they keep winning titles. Still, they looked pretty average in Rio. So if we can't count out Venus and Serena, how can we count out Tom and Drew? Special athletes are special athletes.

But here's the thing. I don't play fantasy swimming or fantasy tennis, and neither do you. I can cheer for them (especially when they represent my country) but there's no trophy on the line for me. I recognize that modern athletes are doing things that nobody their age did before, and the very best are excelling even later in life. But age catches up to everyone. Youth matters.

At some point, super-human players look, well, human. In a redraft league, you have to decide if it's this year, or if they have another good season in them. Sometimes it's a gut feeling, and you have to decide how much weight to give it. So if you feel a certain way about a player, go with that. Trust your instincts.

For me, I probably won't have Brady or Brees. I get the upside, but I don't want to be the one holding the bag if this is the year they fall off the fantasy map. There's risk in giving up their potential, but I don't want the risk of believing in them one year too many.

And when it comes to Matt Forte and Arian Foster, I'll pass. Someone else will take them long before I do. I just don't have enough confidence in them.

So that still leaves Adrian Peterson. My head says he's on a pretty good team and should have a very good season. Why wouldn't he? But for some reason, I expect a significant drop-off. Would I regret choosing Gurley, Elliott or even Mark Ingram over Peterson? How about going in another direction and settling for Doug Martin or Eddie Lacy later? Could I really pass on last year's rushing leader when he still looks this good?

Probably. He's 31. Of course, as I'm finishing this column, 31-year-old Michael Phelps just won his 22nd gold medal. Phelps is the oldest swimmer in Rio. The average age for a swimmer in Rio is, yes, 22 (Gurley's age). Does anyone out there understand numerology? Is someone trying to tell me something? In any case, if my decisions cost me in December, I hope yours bring you gold.

Which old warhorses are you putting out to pasture? Which ones do you think still have another few races in them? Share your thoughts below.