The etymology of the word stripling is uncertain.
Most authorities suggest that it is derived from the noun strip, “a narrow piece of substantially even width,” plus the suffix -ling, “one having some specified attribute.”
This derivation is based on the use of stripling as “a youth, not yet having filled out in manhood, hence, one slender as a strip.”
However, the best authorities then immediately point out that strip, as a noun, was not recorded in the language until more than a half-century after the first recorded use of stripling.
The verb to strip, to divest someone of something, though, is much older, and it seems remotely possible that stripling may have originated with the sense of beardless, i.e., one stripped of his beard.
This is not too likely, since presumably such a person never had had a beard of which to have been stripped.