A lot of people don’t realize that Roger is essentially an older version of Luffy. It’s likely that Luffy will grow up to have a similar personality in the future.
Right now, Luffy doesn’t really care about romance or women because he’s still very naive and clueless when it comes to love and sexuality. He’s like a kid who hasn’t developed that side of himself yet. It actually take someone like Usopp to trigger that awareness in him cuz we’ve already seen moments where they both reacted to Nami in those types of situations. (Luffy nosed bleed twice when he saw nami naked body)
As for Zoro, he might be asexual, or at least emotionally detached from those kinds of feelings. He seems to be aware of it all but chooses not to be affected. Still, in my personal headcanon, I imagine he and Perona may have had something going on during those two years of training.