It's difficult to know precisely, mainly because there is no guarantee that all notes are in an "x" or "y" relay, for queries I like to use nostcat (https://github.com/blakejakopovic/nostcat), querying by your key in the Snort relay I found this note to be the oldest (I believe it is not ordered, so I changed the value of until to bring the smallest amount of notes possible)

nostr:note1fve08l8rpths8qxtfdwrrvgkcqc6getjg9r3pd8ezq497ugu70jqw60few

You can try this strategy for other relays and get as close to the correct result as possible. (there's probably an easier way, but that's all I could think of)