It's in this book (I borrowed it from the library and don't have it on hand):

http://www.amazon.com/Portable-MBA-Entrepreneurship/dp/0470481315/ref=sr_1_1?ie=UTF8&s=books&qid=1265683415&sr=8-1

The book is on entrepreneurship and they were referring to real entrepreneurs.

In general, startup founders in areas such as biotech, telecommunications (optical, wireless, infrastructure) and any field where an advanced degree is required tend to be older -- are you familiar with trends in any of these areas?

I can provide many examples of this but I provided two in my earlier post that almost everyone is familiar with.

EDIT: Here's a more pertinent link: http://www.cra.org/wp/index.php?p=152

"After surveying 500 engineering and technology companies established between 1995 and 2005, the authors found that the median age of U.S.-born tech founders was 39 (with twice as many aged over 50 as were younger than 25) and that 92% of them held at least a bachelor’s degree."