You can find all data on the IANA webpage at https://www.iana.org/domains/root/db or just query it with whois.
.CZ
is listed as created on 1993-01-12 and .PL
on 1990-07-30
You can go back with some in 1985 like .UK
or .US
.
.SU
had a complicated life because, as a ccTLD it should not exist anymore as the country it represented does not exist anymore. However for non technical reason, it subsists. You can find some discussions there : https://www.icann.org/news/announcement-2-2006-12-05-en
But who have rights to become a maintainer of national domain?
This is a complicated question, and not a technical one nor a programming one.
In short, IANA uses the ISO list on country codes (with some exceptions, like .UK
and .EU
) and takes input from the relevant government. Now the problem is that some countries are not stable, and also change. So there are a lot of complicated cases. Some ccTLDs are also marketed as non ccTLDs (like .CO
or .TV
) because the government decided to give its management to some external companies, for some financial agreement.
"Mistakes" happen also, see for example https://medium.com/@Oskar456/stolen-sk-domain-717e070f6735
You can find more about the IANA process at https://www.iana.org/help/cctld-delegation
Each IANA decision to delegate a ccTLD to a country is associated with a "IANA report" listing the justifications. You can read them for whatever country you wish at https://www.iana.org/reports, like a recent one for .TD
for example at https://www.iana.org/reports/2018/td-report-20180227.html
The core business is codified, before ICANN even existed in https://www.rfc-editor.org/rfc/rfc1591
IANA adheres to that, and you can find further documentation at https://www.iana.org/domains/root/help
For more details in general, I would recommend you to read my extensive reply to a related question about TLDs and wars: https://superuser.com/questions/1332236/what-happens-to-country-specific-tlds-in-a-war-involving-that-country/1332238#1332238