I think Whitebeard has become the perfect example of old age affecting power. In the war, Marco told us (readers) that Whitebeard should have been able to dodge Squard's attack, but now he's too old. In the past, Whitebeard must have been such a BEAST that no one would dare challenge him, except Roger. That's why Crocodile mentions all the "Silver medalists" that would come out of hiding when Whitebeard dies.
If the Gorousei were so powerful, they'd be like the current admirals, kicking ass. But instead, they are just political powers. Kong, Sengoku, and Garp also realize the affects of their age, so they don't fight aggressively either (Kong didn't even participate in war).
I was wondering if the disease that Roger had was related to the effects of aging, although probably not intuitively. Perhaps, Roger's disease was such that as long as Roger got stronger and and his will kept being stronger than his disease, he would live. However, if his will becomes weaker, he will die. He was already past fifty when he died, and probably peaked in his power, because his age would weaken him. The disease, however, doesn't peak, and would soon catch up and kill him. That's probably one thing that motivated Roger to turn himself in. Thinking about it, maybe Hiruluk cought the same disease, but he died much earlier.
As for the Sakura trees that mesmerized Hiruluk, that inspired Hiruluk to become a (quack) doctor, and probably removed the negativity and doubt that made him a thief. It also removed his incurable illness, temporarily. We would probably see more of this happening, possibly in the New World.
The question is whether Roger had seen those trees or not. I think he has, and may have extended his life, but not forever. And if they could increase life and remove disease, they would almost be the panacea that Chopper is searching for. Now Chopper would have to make medicine that surpasses this.