It's true that erectile dysfunction is more common in older men, but many potential Viagra users are hardly senior citizens: About 40% of 40-year-old men in the U.S. have some degree of erectile dysfunction. Most Viagra users today, according to Pfizer, are in their early to mid 50s. So it makes sense that the company would want to reach more men. 30,000,000 men in the U.S. use it.