Although personal initiative is vital for entrepreneurial success, we still lack a theoretical model explaining dynamic changes in personal initiative in the context of entrepreneurship. Due to the aging work force in many countries, the question of how age influences personal initiative becomes increasingly relevant. Based on the lifespan developmental perspective, we suggest that age positively influences personal initiative in the entrepreneurial startup process. We hypothesize that there are two mechanisms through which age affects nascent entrepreneurs’ personal initiative. First, age influences personal initiative through its positive effect on domain knowledge. Second, age increases personal initiative because older workers show a higher level of personal involvement. While extrinsic motives like compensation play a major role for young workers, intrinsic motives like personal involvement become increasingly important as people age.