In reply to rogerwebb:
In Irish, Tir na nOg, is the land of the young. And a sean bhean is an old woman. So Tir ná Sean probably is literally the land of the old.
I don't know about Gaelic but Irish is a marvellously lyrical language. So the land of the old could be quite different from the land of age.
The problem's a bit like translating poetry. Often direct translation doesn't convey the feeling of the original. My gut feeling is that the land of age is what you're after rather than the land of the old, per se.
Caveat: No Gaelic, only Irish (similar - or not?), a silver fainne for proficiency, which I didn't deserve and that was, oh no! 50 years ago.
Probably best then to disregard the above as nonsense. It sounds like a great day out on the hill though and that's what really matters.
Mick