Hmmm....NEVER. Honestly, being grown-up is 2 things: 1) some mystical faraway concept we generate as kids with delusions of grandeur about being able to do stuff like drive, not have a bedtime, and become things like firefighters, astronauts and such; 2) once you become "of age" you realize (hopefully) that being grown up is a mindset for people who have nothing more interesting to do than mundanely slog through life. You know, boring people.

As long as you have passions, dreams, and love, you never really grow up.