Well, and the older Anakin kind of matches up better with Obi-Wan's age in ANH. To make the prequels line up well, you have to imagine that hard Tatooine living took a real heavy toll on ol' Ben's appearance. And maybe it did. Or maybe it wasn't all just from suns and wind; maybe he got Mad Bantha Disease in 17 BBY and was never quite the same after. But I don't think many people looked at Alec Guiness, subtracted the dark times (if we even knew how long they lasted in those days?) and came up with someone who looked like Ewan McGregor in ROTS, either.