A recent blog post from the Kauffman Foundation puts it succinctly, when it tries to dispel the myth of the twenty-something tech wizard as the prototypical entrepreneur.
Citing research, they write:
In reality, the highest rate of entrepreneurial activity belongs to the 55- to 64-year-old age group over the past decade. And most high-tech founders are well educated and married with children.
This is in stark contrast to the meme that the young, college dropout is the model for the modern day successful entrepreneur.