How do we know that during Biblical times, Jewish young men wore earrings?
The Torah relates that when the Israelites saw that Moses is delayed in returning from the top of Mount Sinai, they approached Aaron the High Priest, and demanded "Come, make us a god who shall go before us." Aaron asked them to give him all their gold earrings, and after taking it from them he cast it in a mold and made it into a molten calf. That's how the Golden Calf was created.
But notice the details in Aaron's answer:
פָּרְקוּ נִזְמֵי הַזָּהָב, אֲשֶׁר בְּאָזְנֵי נְשֵׁיכֶם בְּנֵיכֶם וּבְנֹתֵיכֶם, וְהָבִיאוּ אֵלָי
"Take off the gold rings that are on the ears of your wives, your sons, and your daughters, and bring them to me." (Exodus, 32:2)
So the fad of young men wearing earrings is nothing new; as stated explicitly in this verse, it dates back to Biblical times.
But you can be sure that this will not convince today's rabbis who oppose this custom. In fact, they will probably use these very verses to point out this is egregious behavior: "Look what wearing earrings led these people to. . ." :)