Like it says, when did you realize you were an adult in your life?

I noticed the other day that I was acting like the old man I said I never would. Turning down parties and such because I had work, or planning a schedule.
I even have a calendar.

Did any of you ever reach a point when you said "Woah, I'm acting like my dad." or something similar?

Obviously I wanted to make a more impressive post, but the words are escaping me right now.
I'm in a hurry, but I wanted to ask before I forgot. :p