Idiom question: has anyone ever heard “even a demon is beautiful at 18” or something similar?

Back when I was first learning Japanese, I remember coming across a text that claimed that a common idiom was" even a demon is beautiful at 18" with the implied meaning being that youth can cover many flaws.

However, I recently picked up studying again, and I can't seem to find this idiom in use anywhere. Has anyone heard this? Am I perhaps looking for too direct a translation?

by frill_demon