I love reading the biographies of great entrepreneurs. They give me courage, ideas and motivation. When I first got started in small business, I viewed them as a form of mentorship.

Heck, I still do. There is nothing more exhilarating than poring over the stories of the men and women who turned their business dreams into reality by dint of dreaming and good, old-fashioned hard work.

Take Walmart founder Sam Walton, for instance. One of my favorite anecdotes about this visionary comes courtesy of Jim Collins and took place when Walton was in his 60s. It's a simple tale, but profound in its implications for anyone who aspires to entrepreneurship. I read it just once, but it stayed with me ever since. It goes like this.

Walton is visiting some friends in Sao Paulo, Brazil. One morning, he wanders off by himself to do some sightseeing. That afternoon, his friends are surprised to receive a call from the police. Walton has been arrested. His crime? He's been crawling around various retail stores on his hands and knees measuring aisle widths.

In other words, it isn't enough that this old, white-haired billionaire has conquered retail in the U.S.--he's burning with curiosity to see what his South American brothers and sisters are up to.

What his story means to me.

I don't know about you, but to me there's something thrilling about that. I want to be that way in my sixth decade. I want to be consumed with passion about nitty gritty details of my trade.

In a recent HBO documentary about Steven Spielberg, the legendary director says that "not losing the child in you is what keeps you young."

That's precisely what I see when I imagine Walton excitedly exploring some nameless store in a far-off land: a man who has not allowed his inner child to die.

The life of Sam Walton provided me with three main takeaways on the subject of how to stay inspired:

1. Learn from everybody.

"[Y]ou can learn from everybody," says Walton. "I didn't just learn from reading every retail publication I could get my hands on; I probably learned the most from studying what John Dunham [a rival] was doing across the street."

Read as much as you can. Take advantage of every spare minute, it doesn't matter where. Airports, restaurants, grocery stores--if you have an idle moment, fire up your phone. Absorb that article. Devour that podcast.

Study people, too. If you admire Sally for her people skills, dissect what she's doing right. If Jake seems to flounder when it comes to setting goals, analyze his weaknesses until you understand them.

2. Keep track of what you learn.

Walton was famous for carrying a little voice recorder around to keep track of his observations. It's a time-honored habit of poets, artists, scholars and explorers--people who are serious about expanding their minds.

Develop a process for cataloguing your discoveries. Whether you maintain a nightly journal or scribble in a pocket notebook, make a conscious effort to retain your hard-won lessons.

They're of no value to you if you forget them, and relearning the same principle over and over again is tiring. Commit to maintaining a record of your ongoing education today.

3. Never stop learning.

Walton launched Walmart when he was 44. He was as avid to grow in wisdom and expertise then as he had been when he began his business career almost 20 years earlier.

Age is just a number. At my company, I rub shoulders with a whole spectrum of birthdays--baby boomers to millennials--on a consistent basis. This has taught me that youthfulness and youth are two very different things.

The latter you can't help. You were born when you were born--blame your parents. The former, on the other hand, has nothing to do with physical years and everything to do with the intellectual enthusiasm and curiosity you bring to the table.

Stay on fire. Be hungry for information. Study the lives of giants and ordinary people alike. As you do, you'll feel your energy expanding, and the passion you bring to your business and personal life will delight you.