It's been more than 40 years since I graduated high school — and a lot has changed since then. I'm older, wiser, wealthier and much more successful. I've built a multimillion-dollar business and am the CEO of seven privately held companies. But there's always room for improvement — even at age 61. In order to do that, it's important to acknowledge past failures and learn from them. Looking back at my 20s, there was so much I didn't know about money. With what little I earned, I wasted on useless things that didn't benefit me at all. Here are the top four things I regret spending my time and money on:

1. Drugs and alcohol

If I could go back in time, I'd tell my younger self: "Your education doesn't stop after college." After graduating high school, I became obsessed with all the wrong things. I spent money on drugs and alcohol — and even developed an addiction problem. I should have been spending that money on things that would help me develop new skills, gain knowledge and make powerful connections. In the real world, your high school diploma is useless, and your college degree won't get you very far if you don't have the right skills to keep up with the marketplace. Investing in yourself will only make you more valuable and increase your earning potential. I didn't realize any of this until much later. At 25, I spent my last $3,000 on an audio program that taught me about sales and how to close deals. I can honestly say that the investment and commitment to go "all in" are the reasons for my success today.

2. Traveling

Kevin O'Leary says that taking a gap year to travel is a bad idea — and I couldn't agree more. I took so much time off early in my entrepreneurial career that it almost derailed me. I was also spending money I didn't have on airfare, hotels and food. A lot of millennials today find themselves in a similar position. They have the urge to travel because they have no purpose at work. They believe time off will help them find that "something" that's missing in their careers. When you don't know what you should be doing, it's easy to put life on hold, go backpacking, stay in hostels and eat ramen. I'm not saying you can't ever take any time off. I can travel the world in my own plane today because I ultimately decided to put in the hard work. Get obsessed with your purpose, and you'll find that your travel plans can wait. Comfort is the enemy of abundance. Don't let an $800 ticket to Europe get in the way of your freedom.

3. Sleeping in

When you're young, it's easy to be lazy and not feel guilty about it. But guess what? The rich and successful get a good night's rest, but they don't sleep in.

Let everyone else in their 20s sleep like they're rich. You should be up at the crack of dawn.

One of my biggest regrets was not taking advantage of all the hours in a day. I allowed myself to feel content when I should have been mapping out my goals and figuring out how to achieve them. Had I realized my full potential in my 20s, I would reached my first million a lot sooner. Let everyone else in their 20s sleep like they're rich. You should be up at the crack of dawn. Speed is power, and when you're young, patience is not a virtue. Today's marketplace is changing at the speed of light, so you need to be nimble to get ahead.

4. Being too comfortable in my jobs