Tom Brady of the New England Patriots is 40 years old. He's the fifth-oldest player in the NFL (and the oldest besides kickers and punters), and a sure-fire future Hall-of-Famer, with five Super Bowl victories.

After a truly amazing performance on Sunday, he's also the number-one quarterback in the league this week. Not bad for a guy who's older than ESPN, the space shuttle, and eight of the NFL's teams.

Maybe you're not into the NFL. That's OK, because this article isn't really about sports. Instead, we're using Brady as an example of how top performers in any field develop personal practices that enable them to achieve reliable success.

Brady describes several of his personal rules, especially relating to diet and exercise, in his new book, The TB12 Method. The book technically goes on sale Tuesday, but there are previews and reviews in The Boston Globe and other media.

The 20-Minute Rule

Brady's diet and exercise regimen is pretty close to legendary at this point. Each day, he begins his workouts at about 8 a.m., and he says that within 20 minutes of finishing, he insists on drinking a protein shake.

"Wait any longer," Brady writes, "and your body will begin seeking its own protein sources and start tearing down muscle you've just been building up."

It's also worth mentioning here Brady's adherence to another popular diet trend, which is to avoid foods that are white or pale in color.

"My nutritional regimen may seem restrictive to some people, but to me it feels unnatural to eat any other way," he writes. "Many people have conditioned their bodies to a nutritional regiment made up of lots of white or pale-looking foods--french fries, potato chips, white bread, chicken nuggets--that don't exist in nature."

The 20-Ounce Rule

This one is pretty easy, but it seems religious. The first thing Brady says he does each morning is drink a 20-ounce glass of water.

(As it happens, my wife does this too. "I started to do this when I was working with a nutritionist," she explained to me, as we sat on the couch together while I wrote this article. "It's a good way to get your metabolism going.")

The Globe reports that Brady talks about hydration "at length in the book," and "says he drinks 12 to 25 glasses of water a day, always with his TB12 electrolyte concentrate added."

The 12 to 25 Glasses Rule

About those 12 to 25 glasses of water: That works out to between two and four gallons of water over the course of the day. Making it even trickier is that Brady says he tries not to drink much water with meals.

Reason: He believes it interferes with good digestion.?

"Drink water half an hour before a meal, and then wait an hour before you have your next glass," he writes. Beyond that, he basically has to drink water constantly.

The 20-Percent Rule

We're back to the specifics of Brady's extremely strict diet. Besides his hydration dedication, he identifies three key dietary principles, that all have to do with what foods to eat (or not) with other foods:

First, he doesn't eat carbohydrates at the same time as proteins.

Second, he limits "acidifying foods" ("like white rice and bread, but also cold cuts, pineapples, and yogurt") to 20 percent of his total diet. "The other 80 percent he says should be made up of alkalizing foods, like Brussels sprouts, sweet potatoes, and dandelion greens," according to a summary.

Finally, he doesn't eat fruit at the same time as other foods.

The Positive-Thinking Rule

Brady says he wants to continue playing football until his mid-40s, at least. That's not exactly unprecedented, but it's rare--and it's rarer still to continue playing that late in life and remain a top performer.

It's not possible without believing that it's possible, which is why Brady comes back repeatedly to how he works to maintain a positive attitude. I think it comes through especially well in two excerpts:

I make the choice to remain positive. That is something within my control. I don't like to focus on negatives or to make excuses. I am never a victim. I gain nothing if I get angry or frustrated. You can make life a lot harder for yourself by focusing on negative things ... or making excuses for why things didn't go your way. ...

Every year, people like to remind me that another 12 months have gone by, and that Father Time is undefeated. ... [R]ealizing that has made me continually rethink my approach ... [G]etting older has been a positive experience athletically.