This was late USSR, all the way up to its dissolution and privatization of housing in 1991. I was a small kid at the time, but I don't recall the standard being different depending on age.

The allotment of living space (counted as bedroom area per person) varied depending on the city, and sometimes there was a difference between the nominal and the actual number. In Moscow and Leningrad the designated minimum was around 7 m^2 per person, but in practice applying for a new apartment would be unlikely to succeed if you had more than 5 m^2. In some of the provinces, it could go as low as 3 m^2 per person.

And keep in mind that this is the minimum that entitled you to apply for a new apartment. Which means that you'd be put in a line to wait your turn to actually get one when one is available, say, 10 years later.