Just how old is Roland supposed to be?

I mean I know time has gone all funny in his world and whatnot but that taken into consideration, what visible age is he supposed to be? There’s one instance where something he’s doing “makes him feel 40 again” so can we assume he’s at least 50? Maybe 60? Again I know the actual count of years may have slipped as the world moved on but he has to have some ballpark outwards appearance. When actors are suggested here for the role I see a lot of replies that are like “too old” but are they really? I’d say actors who are between 55 to 65 would sort of fit the bill just nicely and ones who are still 45-50 would feel almost too young unless they were appropriately grizzled enough.