Just going out on a limb here with a guess, but would בחור be considered more "teen to young adult" age, whereas ילד would be more "young child to preteen"?
I've been told that בחור has no limit, if the person speaking to the בחור is older than him. For example, I'm 51, and the old guys at my synagogue call me "young man" sometimes ;-)
Does בחור mean post-Bar Mitzvah? I would be grateful if anyone could help with this.
It means about age 13 to 30. One the girl reaches 18, It should be translated as young woman.