This is much more well defined than you try to argue. Your main argument is basically your ignorance of much of political theory for the past two centuries at least...
What about 17 year olds? They don't get to vote, so by your definition, you don't have a democracy.
Drop the voting age to 16, as some propose? Then 15 year olds still don't get to vote, so you still don't have a democracy.
More serious: foreign nationals who live in the same country aren't allowed to vote despite paying taxes and being subject to the laws. More serious still: Minorities and in general "Democratic" voters are kept from turning out by discriminative voter suppresion. That's a deficit on democracy. Or when you incarcerate a ton of people, especially with racial preference. Or when you take away bodily autonomy from women with a ban on abortion, when men cant get pregnant and have more ways to extricate themselves of those consequences. Black and white thinking is not the way
What are “democratic values” though? A lot of people seem to use the phrase to mean whatever values they personally endorse - but what makes those values “democratic”? How do we decide what values count as “democratic”?
> Easy examples: Killing off a minority.
I think “genocide is wrong” is a value which the vast majority of people share. But what makes that a democratic value?
Same point about all your other examples - whether the values you support are the right ones or the wrong ones, what makes them “democratic”?
In a pure majoritarian democracy, whatever the majority wants, they get - even if they want something bad like genocide. Of course, I don’t think genocide is right, even if the majority wants it - but that’s not a “democratic value”, that’s a case where some values (such as the wrongness of genocide) are more important than democratic values, and ought to win out when they conflict with the value of democracy.