I'm not there yet. I guess this all depends on how one defines adult. Sure I deal with responsibilities such as paying the mortgage, and I keep studying things, not for grades but because life (for me) is a quest for knowledge and there's always more to learn, but I don't think I'd call myself an adult.

There are still more questions than answers, and it seems to me that if you can still approach the world with wonder you don't have to grow-up. Because really we never stop growing. Ideally we're always moving forward, so I don't know how one could define an end point to that process, at least not whilst still attached to this mortal coil.