I think there is some commonality in the skills you use as a PM and those you would use as an entrepreneur or business manager - all those skills that you use to coordinate a team to focus on achieving a goal.
Starting up a business might be considered a project, but running a business is different; I think it's even more than a continuous series of related projects. The part outside the project is understanding the market your business is in and creating strategies to compete in that market.
Project Managers (at least in the projects that I have been involved in) get involved after the strategies have been created - sometimes even after the objectives for a project to execute that strategy have been outlined.
Now... that said, if you have been around long enough you'll have seen a number of successful projects that just didn't work because the underlying strategy was just wrong. As an experienced PM you might eventually start thinking "I could run things so much more successfully" - I haven't made that transition myself, but I am close to people who are employed by poorly run businesses and I definitely get the feeling that I could do better. You might feel that way too and if your PM experience has helped you learn from other people's mistakes you may be right. Even so, I think you would find yourself using a very different skill set much of the time.
As an anecdotal reference... I know of two good Project Managers who own restaurants. One is by all appearances successful, the other unfortunately was not.