That picture is from an article comparing other presidents. Why has he aged so much? Whatever your political ideology, you have to agree that these past four years have been some of the worst in recent memory, and it shows on the president's face.
Now think about people like Kim Jong-Il, Fidel Castro and Robert Mugabe, just to name a few. All these men are brutal dictators that have been in power for years without it affecting their health. Granted, Castro and Kim are no longer in power, but look at how long they lived and how well their health was. I have a theory as to why this is.*
I used to volunteer at the San Francisco Zoo when I was younger. Whenever someone asked you what the lifespan for a particular animal was, you had to give them two answers: in the wild and in captivity. Most people know that animals in captivity live longer than their wild brethren. The same principle that keeps animals in captivity alive keeps brutal dictators healthy.
Kim lives a life of opulence while his people starve to death. He eats like king and lives like a prince. He is pampered beyond compare but unlike a real leader, he does not have to worry about political opposition or even a revolution. He lives the life of a panda in captivity.
Compare that to Obama's life in "the wild." No matter what choice he makes, someone is going to get mad and will want him out of office. Wether it be attacks from republicans or uncooperativeness from democrats, Obama's job is never done. He's a zebra in the wild, ever vigilant for the next threat.