As adjectives the difference between youthful and youngly
is that youthful is young or seeming young while youngly is (obsolete) like a young person or thing; young; youthful.
As an adverb youngly is
(obsolete) while young; as a youth.
youthful
English
Adjective
(
en adjective)
Young or seeming young.
Characteristic of young people.
Synonyms
* lively
* sprightly
* spry
* young
Derived terms
* youthful river
youngly
English
Adverb
(
en adverb)
(obsolete) While young; as a youth.
- And that fresh blood which youngly thou bestow'st — Shakespeare.
Adjective
(
en adjective)
(obsolete) Like a young person or thing; young; youthful.
- (Shakespeare)