Asexuality or immaturity?

My closest friend is eighteen years old - she thinks sex is absolutely disgusting, talking about sex around her makes her cringe and go all red in the face. She even thinks kissing is gross. She will say 'Oh my God - so and so is so hot!' and flirts with guys quite often (when asked if she is interested in someone she just says "I don't like him that way - I just like flirting with him") but she claims she has absolutely no desire sex, kissing or a relationship whatsoever. Is this asexuality or just part of her immaturity? (she does have the maturity level of a 5th or 6th grader to be honest.) I don't know - I just don't really understand it.