I'm not sure what you're saying, but I'm very likely to live in a city older than yours. Buildings hundreds of years old are castles, churches or a limited number of inner city monuments. They are very hard to live in, let alone live comfortably in; they are very expensive to retrofit and in general nice to look at but a pain to live or work in.
Buildings 200 to 100 years old are more common, but still suffer from many defects; unless renovated in a way that is essentially 'build a new house inside the old one'. Which is more expensive than knocking the old one down.
Anything less than 100 years but older than say 20 can be made to 'modern' standards, for some values of 'modern'. It won't be nearly as comfortable as a new house though, again unless renovated the expensive way.
Housing needs change. If you think we Europeans build for 100+ year use, you obviously know nothing about real estate or construction, and the history thereof. If you think the fact that we have a bunch of old buildings is because they were designed that way, you are very mistaken.