Motivation for the question: Let's say my son is describing to me something that was said at school, and I'm finding it hard to figure out whether it was said by some adults or by some students. (Children's descriptions of things that happened at school can be a bit hard to follow sometimes.) I ask
Espera, ¿quienes dijeron eso, los muchachos?
Sometimes at this point he gets hung up on gender, thinking that I'm trying to make a distinction about boys vs. girls. I've explained to him that terms like "los papás," "los padres de familia," and "los muchachos" encompass both genders unless the context suggests otherwise. In other words, in Spanish one assumes that these terms include a mix of both genders. But I would like to understand better the boundaries of this assumption.
How far does this assumption go?
Does the assumption ever extend to the singular, as in English? (For example, "He who hesitates is lost" and "When a party enters into a rental agreement with a tenant, he has certain rights and responsibilities" apply just as much to women as to men.)
Edit -- clarification:
I'm not asking about how to express myself. (I believe I explained my thinking about that in the question, and it aligns with what you wrote.) And I'm certainly not asking about translating. I'm asking about how the meaning is taken in various contexts upon hearing (1) the masculine plural in a general (ambiguous) context; and (2) the masculine singular. Regarding the latter, obviously in aphorisms (dichos), the masculine singular is taken to represent humankind. But what about conversational remarks?