Calling those "democratic" is a stretch though. Most of the time, it was election by a few grandees, with the son of the previous monarch elected in almost all cases. The Poles are sort of an exception due to the way they decided who was noble. (All the sons of a noble were nobles, so in the end something like 10% of the population could vote).
Yeah, but if we're being picky and saying "it's not a democracy unless everybody is allowed to vote", Athens weren't democratic either, the US wasn't a democracy until whenever women and/or black people were allowed to vote (whichever was layest) and Switzerland wasn't a democracy until like the 90's when the last Canton gave women suffrage. Would I call them a modern democracy? Of course not. Were they democratic systems of their time? Yes, I would say so.
You are also forgetting that the further back you go, the looser the boundaries of nobility go. "Landed gentry", and the distinction between in and unlanded nobility, is a notion that grew over time - in the early medieval days and earlier, nearly all nobility was unlanded by default, and land titles were appointments that were not inheritable.
This continued to be true for areas such as the North that never went feudal. In Sweden, for example, where 99,99999% of all people were free men, the distinction between nobility and commonry was very ceremonial.
The thing is with the king of Poland, he had less powers than, say, the president of the US. The seat was mostly ceremonial after 1700 and essentially nobody ruled the country. It was utter anarchy and to use the "Golden Liberty" as an example of a functional democratic system is hilarious. Democracy pulled one over Poland.
And, just as off topic, nobility was comparatively easy to bang into, because a child of any noble (regardless of gender) was a noble. This meant if you married an impoverished noblewoman, your kids would be noblity and they'd get the noblewoman's family coat of arms.
The greeks had hereditary kings in the early period, before they turned to non-hereditary dictatorships and early republics, didn't they? Were the northerners electing kings before 1000BC?
We are unable to know it because of the lack of historical accounts, of course. All we can do it extrapolate backwards from later accounts and guess on how far back it went. The almost universal appearance of such customs in Germanic cultures seems to suggest that they at least precede the Germanic migrations.