I was banking several thousand every summer from 4th through 6th with a pet sitting gig that I did. It was really simple and took about 15 hours a week. My father owns three companies, my mother owned one, they were and are all incredibly successful with the exception of one, which has just stopped losing money. My grandfather owns one that it probably far more indicative of how a business normally ends up. He lives a middle of the road middle class life, and probably puts in 60 hours a week minimum. My mother and father put in 50-80 for years, even when they hit it big.
I'm not going to go in to details on the companies, but starting a company is not for the faint of heart under most circumstances. Owning and running one aren't either.
Here are some things to keep in mind:
-Don't start a restaurant or club unless you are a masochist (and a rich one at that)
-Don't start a company because it's glamorous- ferrari dealership, motorcycle dealership, take your pick, etc. They're money pits.
-Don't go in to business with a friend
-Expect to work harder than your employees
-The money and life that people think of when they think of company owners happens after you sell that bitch. You won't be taking many vacations.
-Multi-millionaire is meaningless when you aren't watching your expenses.
-The above people make for cheap and profitable acquisitions
-Learn basic accounting and get good at finding patterns. Gut instinct on accounting because something didn't look quite right at first glance has saved us millions.
For starting up you're going to be more successful if you're fairly personable. Start networking like a motherfucker. Word of mouth and favors are generally required for a company to make it the first couple of years. Also make sure that you patent everything. If you live big right now, I'd move to a smaller place and start pocketing emergency money. Expect to spend out of pocket on your company, and make sure that you're passionate about it- the strain on your marriage, parent/child relationships, friendships, etc. won't be worth it otherwise. Also know that you're doing something that 90% of the children of business owners would never do.