Multae is feminine, Multi is masculine.
So, multae iuvennes would mean many female youths
Where as multi iuvennes means many male youths.
No, iuvenis is always masculine. I have never, ever, seen it used for a female in authentic texts.
Doesn't iuvenis mean youth?
Not exactly. It means young men. It was a different time. Women didn't have rights. When Romans talk about "iuvenis," they are always talking about the men.
I think so.
Oh that makes more sense.
Why "multi iuvenes" and not "multae iuvenes"?
iuvenes means young men and its a masculine noun (a concept which might be foreign to you if youre an english native speaker). Multae is at the feminine gender, while multi is masculine, so multi goes with iuvenes.
Is many young men singular or plural. Should it be habitant?
Habitant" on its own means they live/are living since it refers to the young men.
the answer is already there. I see this problem often.