It's not just the president who is visibly older than he was when he took office in 2008. According to demographic data from National Journal's Decision Makers report, his underlings have aged as well.
It actually may be something of a myth that presidents and people in high-stress jobs age faster than the rest of us. In 2011, the Journal of the American Medical Association published a study that found that presidents actually live longer than we might expect. A full 68 percent of all the Presidents of the United States lived longer than the average man.
But still, according to National Journal's Decision Makers survey of 250 top officials, the average age is now 52, and 25 percent are age 60 or older. In 2009, 18 percent were 60 or older.