How do you be a successful businessman at age under 27?

How do you be a successful businessman at age under 27?
I'm interpreting your question as you wanting to have a successful business by the age of 27. Three basic things: First, follow you passion. Start a business doing something you know and love to do. Something you'd do whether you were paid or not because starting out you may not get paid much. Second, have a plan, a business plan. Carefully investigate your market, pricing, costs, equipment needs, etc. etc. That plan is a guide on paper, not in stone, so be flexible understanding that barriers, unforeseen circumstance come along that can prevent the business from being where you'd like it to be and then again circumstances can propel your business forward to place you didn't dream possible. The plan is also a way of selling your business to family, friends, the bank, SBA, to obtain funding above and beyond what you are putting in yourself. Third, never forget the IRS. I have had clients who had started their business so they wouldn't have a boss anymore but they seemed to neglect paying the various taxes that are out there and they end up having the worse boss since Attila the Hun, the IRS. One final thing, carefully think about what you mean by success. If success is that you have a business that is on an upward trend and something to be proud of then great. If success is to have $1,000,000 in the bank watch out.