[Zababa]

>For kids that was a way to decide who is going to fetch the water for the table (smaller number or higher number of the table).

I only knew the version where your age is the number on the glass. For fetching water, it was the slowest person to say "pot d'eau" (water jug) and sometimes put a hand to your head (it depended on the group).

[Broussebar]

I might have generalized then. It’s maybe something that we had only in the south (aka the broc à eau area). We also used it to check our age of course.

[WawaFin]

no I was in IDF and the glass gets your age and the oldest or youngest had to fetch the water, so it not only in the south