Warsaw: ztm.waw.pl/?c=142&l=1
- any person that is at least 70 years old uses the city public transport for free, ID card or any other document with a photo and the birth date is needed
- pensioners below 70 years old are entitled to a 50% discount, document: pensioner ID or a bank printout showing that the person gets a pension
In both cases it doesn't say that it must be a Polish or Warsaw citizen, so foreigners are also entitled.
Wrocław: mpk.wroc.pl/bilety/prawa-pasazera-i-ulgi
- persons from 70 years old up: travel for free, they need to have an ID card or another document that has a photo and confirms the age
- pensioners (in practice - those below 70 years) are entitled to a 50% discount, but a Polish pensioner ID card is demanded
Kraków: mpk.krakow.pl/pl/bilety2/uprawnienia
- as in both previous cities, persons being at least 70 years old travel for free with a document confirming the age and the identity
- pensioners below 70 years old need a pensioner ID card
So, in all these cities, 70+ members of your family can use the public transport for free with a passport or ID card. Those who are below 70 years old and are pensioners - rather not. Remember that, at the entrances to the Warsaw Metro, there are gates, for which you need a ticket to open them, so if you want to use the Warsaw subway, either enter and exit the station using the elevators (then you omit the gates), or follow this advice:
The bottom line is: If you are senior ask for your discount ticket entilement at the customer services centers at designated areas in the city, and they will give you a buspass or entry ticket for the subway.