Presidents, the world over, appear to age faster when they ascend to power than if they had chosen other careers but politics. For a stunning comparative, just check their photos during their swearing in and when they're on their last terms.
Take President Uhuru Kenyatta. He had black hair when he won the presidency in 2013. Now he's graying. He looks tired, like a young grandfather on a steady roast red meat diet and stiff whiskey.