Banmal is relational. Casual speech usually becomes natural through a mutually established relationship. Being older, being the same age, or hearing the other person use banmal does not automatically make a unilateral switch appropriate.

해요체 is a practical polite baseline. Everyday -요 speech works across many ordinary interactions, especially when the relationship is new or the preferred level is not yet clear. Vocabulary and honorific markers still matter inside the sentence.

하십시오체 is more formal, not simply “more respectful.” It fits many official, service, presentation, and strongly professional situations, but using it everywhere can sound unnecessarily stiff. Close people can also change levels when they move between private and professional settings.