In what way is Phoebe’s discussion with Holden (beginning on page 168) mature and adult-like?

Phoebe is Holden’s younger sister and even though she is six years younger than him, it is obvious that Phoebe is more mature than Holden. Some people say that woman mature faster than guys do, but by six years? I think that some of the decisions that Holden has made in his life has affected her also. It is possible that seeing him get kicked out of school has made her more mature because she knows not to disappoint her parents or they get mad. She may have also learned that making bad choices does not help you in life. She exhibits great maturity and even chastises Holden for his immaturity. Like Mr. Antolini, Phoebe seems to recognize that Holden is his own worst enemy. It is remarkable that a girl of such young age is able to recognize her older brother’s level of immaturity.