For some, it's mostly linear; while others encounter more twists, turns, and bumps along the way.
Billionaire Mark Cuban, for example, faced hardship when he first started, writing in "How To Win At The Sport Of Business" that when he got to Dallas, he "was struggling - sleeping on the floor with six guys in a three-bedroom apartment." On the other hand, Starbucks CEO Howard Schultz was a Xerox salesman dreaming of good coffee.
To prove that no two paths to success are alike, we've highlighted what Cuban, Schultz, and 16 other successful people were doing at age 25.
This is an update of a post originally written by Vivian Giang and Max Nisen.