The word flighty is used to talk about a person's character, specifically someone whose moods, decisions, or interests shift suddenly and often, making them hard to rely on. It carries a mildly critical tone, suggesting the person cannot be counted on to stay committed to one plan, opinion, or relationship for long.
The other options misread the word by connecting it too literally to flight. Being light, loving flying, or flying kites all draw on the surface similarity between flighty and flight, but the actual usage has moved away from anything to do with physically flying. It instead points to unpredictable, changeable behavior, which is why calling someone flighty is really a comment on their indecisiveness and lack of dependability.
Given this figurative sense, the correct meaning is indecisive and irresponsible, so option 2 is the answer.