I don't think that's true. Remember that there was a massive post-war boom in population and construction starting in the 50s and extending for several decades

I don't think that's true. Remember that there was a massive post-war boom in population and construction starting in the 50s and extending for several decades until the land got used up in cities. Chances are if you were old enough to rent an apartment or buy a house in the 70s, it was built within the last 20 years.