Americans have a list of important ages. At 16, it's time for a driver's license in most states. At 18, it's time to register to vote. At 21, people can buy alcohol. At 25, auto insurance usually gets cheaper. The next watershed date in a person's life after that is probably age 65—the minimum age most people sign up for Medicare. 

Thanks to Medicare, millions of American seniors have access to health care. And while the program seems to go through an annual game of political pingpong every time Democrats and Republicans spar over the budget on Capitol Hill, Medicare is a vital part of the American social safety net.

Let's say an employee starts saving for his golden years early in his career. He makes wise financial choices. He lives within his means and gets a little luck along the way. Then, he just might be in a position to retire before that watershed age of 65.