I'm not sure whether by "script" you mean Renpy "scripting"(programming/coding) or actual dialogue. I'd suggest coming up with a non-generic backstory for each "milf" in your game, think about their initial feelings towards the main character, and think about how they might react to the main character doing various things. Also, give them a fairly consistent conversational style. If you're not a native English speaker, it's going to be really challenging to convey whatever nuance your dialogue had in Russian/Spanish/Korean/Japanese/whatever into a foreign language.
Show, not tell with your story. Don't have the milf saying "Oh my god, why am I so horny right now?" Have her look a little flushed in the face, a distant look in her eyes. Maybe later there's a brief scene where she's touching herself, and the MC catches a glimpse when he hears some odd noises.
Women will flirt in both obvious and subtle ways. So maybe she's the verbal teasing type, or the handsy type, or keeps a veneer of decency while subtly putting her body on display for the main character. Seduction is a dance, and it "takes two to tango" as the saying goes. While the MC is making his moves, she's making hers, dependent upon how she feels at the time.
Just a few suggestions. Bon chance!