How do they know the average ages of the E U voters Please?

Answer 1

On a general level and apart from specific ballots, EU countries don't have the US requirement that you can only vote if you register first. Every adult citizen is automatically registered as a voter, too. And since a country knows the ages of all its citizens, they also know the average age of its adult citizens.

Should you mean: how do they know the average age of people who actually have voted in an election, the answer is 'through exit polls'. Ballots themselves of course are secret and anonymous. But researchers sit at the exit of a great number of polling stations, and there ask voters what they have voted a minute ago. The exit polls are still anonymous (no names asked) but people are asked their age, sex, and other background information that might be useful for statistical analysis.

Answer 2

The average ages of EU voters are typically determined through exit polls and surveys conducted during the elections. Polling organizations ask voters their age range as part of the demographic information collected. By aggregating these responses, they can calculate the average age of the voters. Additionally, election authorities might also collect age information from voter registration records to obtain more accurate data on the age distribution of voters.