big enough and ugly enough

Meanings

1. Mature, grown-up, old enough (with the implication that one can look after oneself and make one's own decisions).

Etymology

From the notion that youth, especially children, have a more beautiful and endearing appearance, thus maturity ought to make one not only bigger, but uglier too; though, in some cases, the opposite is true (see ugly duckling and its associated fairy tale, which illustrate such a case).