There's no single "Wonder Years"-like moment that I recall making a grand shift from boy to man, but rather a series of little steps that got me to being (mostly) adult. If I had to pick one of those, though, it would be this:

After college, Heather and I each lived with our parents to save money until about three months before our wedding. While we'd each had apartments in our respective college towns, there were roommates, parents helping out with (or completely covering) the rent, etc. This was our place, with a nice little front lawn and an attached garage and a mysterious neighbor named Phil and everything.

For the first few months or even couple of years, I'd be walking through our modest two-story townhouse, just doing day-to-day things like closing cabinet doors Heather had left open, and I'd think, Where are the grown-ups? And then I'd realize: THE GROWN-UPS ARE US!!!