I did the math recently, comparing Bill Gates and Mark Zuckerberg at the same age.

Let's just say I had a hunch about something I thought Gates might have done at almost exactly Zuckerberg's age now -- something that every successful person needs to consider.

Turns out, I was right. Zuckerberg was born May 14, 1984, so he's now 35 years and 11 months old. 

Gates was born October 28, 1955. And that he means he was almost exactly Zuckerberg's age now, when he met Warren Buffett for the first time.

I'm convinced that this particular date, July 5, 1991, was the most important day in Gates's life. 

There are many other contenders of course: I'm guessing the day Gates met Paul Allen, the day he left Harvard and started Microsoft, and the day he met his future wife.

But in meeting Buffett, Gates found something that many people go their whole lives looking for -- and something that's even more amazing for a person of Gates's success level to have found at that stage in life:

A true, trusted mentor.

The two titans have talked about their relationship many times: their unusual friendship, and the degree to which Buffett guided Gates to see what his second act would be.

Now, thanks in larger part to Buffett's advice, Gates has stepped away from the boards of directors at both Microsoft and Berkshire Hathaway, in order to focus 100 percent on philanthropy and public health.

As a result, he's been in the position to warn for years about the kind of global pandemic we're currently enduring, and to have a worldwide audience paying rapt attention to what he thinks he should do next.

It makes me wonder who is influencing Zuckerberg now. 

Clearly there's Sheryl Sandberg, who has been the chief operating officer at Facebook since 2008. 

There's his wife, Priscilla Chan. Gates wasn't yet married when he met Buffett, and of course Zuckerberg and Chan started their philanthropical work at a younger age than Gates did.

But I wonder if there's anyone else, outside of Facebook and his family, that Zuckerberg turns to for advice and mentorship.

And if not, I wonder if history will repeat itself, and there's someone he'll strike up a relationship with in the next little while.

I think there's a tendency to think that once people reach a certain level of success, they become exclusively the mentors, not the mentees. So I've always been struck by how Gates, already a billionaire in 1991, formed his relationship with Buffett.

The takeway for me is that no matter how old you are, no matter how successful you are, almost everybody does better with a guiding light to look up to. 

So if you're a business owner, or someone who still aspires to entrepreneurship, ask yourself: Who's my mentor? And what's the most important thing he or she has taught me?