Some time around the year 1500, English speakers stopped addressing each other as "thee" in favor of the plural form "you". The singular "thee" is intimate and informal, but might be considered rude in the wrong context. So using the more polite plural form "you" in all contexts is a safer option.

Many young people seem to use the gender-neutral "they" rather than "he" or "she", even when the gender is known and is unambiguous. This may turn out to be a fad, or it may be a similar generational shift in the language.