If the typical person ages one year at a time, the typical president, Dr. Michael Roizen told CNN in 2009, ages two years for every year they are in office.
And it shows.
Take a look at how the last three presidents aged from the moment they took office to the moment they left, or, in Barack Obama's case, through four-plus years.
President Obama was 47 when he took office. He's 52 now.
George W. Bush was 54 when he took office. He was 62 when he left.
Bill Clinton was 46 when he took office. He was 54 when he left.