This is very dependent on location. There are places where, eg, the buildings from the 60s are rather well built, but the later buildings are terrible. It's not the age that matters. My previous apartment was brand new building, but cheaply built to cash in on certain developments nearby (new transport links, new faculty building at the university). I doubt it will still be there in twenty years. My current building is much older but much nicer to live in (thicker walls, better ventilation, no creaks and whistles when the wind blows the wrong way). I think it must be 40 years old or more.