The rate of new business startups has fallen drastically over the last thirty-five years, accelerating greatly since the year 2000. Other measures of business dynamism such as the job reallocation rate are consistent with this trend, raising serious concern given the importance that young, high-growth firms have on employment. The timing of this decline coincides with the start of a steady increase in both the life expectancy and average age of the workforce. I document an individual's propensity to select into entrepreneurship follows a `hump shape' as they age. To account for both individual behavior and aggregate trends, I construct a life cycle model of entrepreneurial choice, studying a number of channels that link demographic forces to entrepreneurial selection. I find that demographic channels can account for a large portion of the recent decline in startup activity. This model predicts that entrepreneurial activity will continue to decline as the pool of potential entrepreneurs continue to age. I conclude with a discussion of the potential policy tools that will affect individual's life cycle risk attitudes and the predicted effects that such measures will have on the rate of new business startups.