Jill's a short form of
Jillian, which is a variant of
Gillian.
Gillian's a medieval English feminine form of
Julian, which is an English form of Julianus, itself of Latin origin. "Downy-bearded" is the correct meaning, but it's easy to see where "youthful" came from: Only young men have downy beards. Older men usually have coarse beard hair.
This site is one the most accurate name sites on the Internet, if not
the most accurate. By contrast, 99% of name sites with the word "baby" or "children" in the title are utterly worthless when it comes to accuracy.
Miranda
"Multiple exclamation marks are a sure sign of diseased mind" -- Terry Pratchett
Proud adopter of 15 punctuation marks. Check my profile for their names.