> "Childish," from the Latin word for "boy."
I think you mean "puerile", not "childish."
"Child" comes from Proto-Germanic. https://www.etymonline.com/word/child says "no certain cognates outside Germanic".
The Latin word for boy is "puer": "a boy, lad (typically between ages 7-14 but could be younger) (older than an infans but younger than an adulescens)" - https://en.wiktionary.org/wiki/puer#Noun_4 .
Puerile comes "from Latin puerilis "boyish; childish,"'- https://www.etymonline.com/word/puerile .
Grammatic gender doesn't always match natural gender even in the European languages. "Wīfman" means "woman" in Old English but is grammatically masculine. The Old English "mann" meant generally "person". https://en.wiktionary.org/wiki/mann#Old_English making "wīfmann" a female person and "wæpnedmann" a male person, though "wer" was the usual word for "adult male" (remaining in "weregild" and "werewolf").
In modern Swedish there is no masculine gender, and "man" can mean either "an adult male" or "a person". Consider "Hysterektomi ... kan också göras om man har cellförändringar eller cancer i livmodern." which in English is "A hysterectomy can also be done if one has cell changes or cancer in the uterus." (from https://www.1177.se/behandling--hjalpmedel/operationer/opera... ).
The Swedish "man" in that sentence translates directly as "one" in English, not "adult male", though usually in English we would write "you" as a sort of third-person pronoun, over the more formal "one" - https://en.wikipedia.org/wiki/You#Third_person_usage , even when we don't know if the reader has a uterus.