Hi, Bex! Hope you’re doing okay :) So, every time someone mistakes Eugene’s age in the movie a part of me dies lol. I think I remember how the rumor of his age begun but I can’t find it anywhere. Do you have it? Sorry if you already answered that before
Boy, that's a mood. And no worries!
Okay, so many years ago, when the fandom had no glimpse of a canonical age for Eugene, and talking to movie crew on social media was in its infancy (I think I aged a decade typing that), people started asking Tangled crew questions about the movie, including Eugene's age.
One person who worked on it (unfortunately, I don't know who it was and have no links to the source) said that they personally felt that he was about 26.
That was all the fandom needed.
It was a number, and it got latched onto. Even when later Nathan Greno and Byron Howard said that they thought he was 22 to 24, but that he had no canonical age, everyone just went with 26. It became so widespread that people took it (and still take it) as canon.