Here's what I wonder about, in the prequals, Obi-wan fled while in his early 30s, then met Luke in the desert approx 18 years later. So would be around 50-ish at that time. How brutal of a life must he have endured in between to have caused him to age that much? Because he looked like he was at least mid 60s - early 70s in Episode 4. To age that much more than would be naturally, would be like having a half dozen ex-wives, all getting alimony & paying child support for a dozen kids that weren't his because they courts believed their alligator tears.
Here's a strange thing I was once told which might be relevant to Ben Kenobi ageing prematurely:
Ran into a guy once who turned out to be a doctor. While chatting about ageing and the ageing process he said he couldn't be one hundred percent sure, but he said an odd thing was he'd never met an elderly person with a wrinkly bottom.
I asked him to explain as I must have misheard him say he'd never met a pensioner with an elderly looking arse.
He said it was true, in his experience at least: The bums and the feet. Not a wrinkle on them, and he said his hypothesis was that it was sun damage which ages the skin, because the bums are almost always wrapped up under layers of clothing and the feet are almost always wrapped up in socks and shoes.
Well, Tatooine has two suns... If the Wrinkly Bum hypothesis is correct my guess is that would be enough to prematurely age anyone, and would also explain Uncle Owens leathery aged appearance - he was the son of the step brother of Anakin Skywalker - considering Luke was the son of Anakin Skywalker himself, Uncle Owen was probably a lot younger than he looked, too. Looking into it he was killed at the age of 52/53.