Howard:
Age or cosmetic appearance? The two are linked.
If you were buying a house, would you rather one that looked clean and tidy or one that was filled with junk and filthy? Any professional will tell you that clean and tidy adds value to houses and cars for sale: it is what the buyer wants.
So clean and tidy aircraft work too: so if old, clean and tidy and get tatty bits fixed.
The customer doesn't know about good maintenance, but they know about clean and tidy!
Deep down, if not clean and tidy, they suspect poor maintenance. They have nothing else to make a judgement on.
On the surface, knowing what I find simply when cleaning aircraft and cars - yes, I have told people thinking of buying an aircraft to offer to clean it for the owner, since they will learn a lot from that! - that dirty/poor cosmetics mean lack of top grade maintenance.