The inconsistent criteria are really rather obnoxious, I agree. Some examples that cought my eye while looking at the map and data
I think that 976 for Austria is correct, as that's the first mention of Ostarrichi, although not as independent country. For Hungary as well, the dates are the ones that should be taken into account, as this was the time when the magyars moved into the territory of what is now Hungary.
To give 1871 as "birthdate" for Germany is of course ridiculous, that should be 843
as in the case of France.
Therefore, if we already use dates like 976 for Austria, we can only stare in disbelief at the fact that Croatia
should be only 22 years old and Serbia
Turkey will certainly be interested why only the modern state after the fall of the Ottoman Empire
and the following war with Greece has been given credit. I think we can safely assume at least 1453 (conquest of Constantinople), or even an older date, if we take into account that most of Anatolia had been undeer turkish rule far before that.
At last, not to get too eurocentric (I'm austrian, so Europe's what I'm most familiar with), Rwanda
was a kingdom (or several closely related kingdoms) with a distinct culture and language long before becoming a (german, then belgian) colony and gaining independence in 1962.