What drove it home for me was remembering back when i was in my
20s, being up a 3:00 am getting pissed. And now being in my 40s,
Just trying to get up at 3:00am just to take a piss.
AAAHHH… the good old days
my first tour in Vietnam as a medic.
The day I realized I got excited about getting a new major appliance (refrigerator, washer, dryer etc…). “Kids” don’t get excited about appliances.
What, I’m an adult?
I still get that feeling from time to time. I’ve been married 4.5 years, have a kid on the way, and I’m a homeowner.
I do have to say that probably buying my house was the real wake-up. I’ve felt like an adult in general since leaving college and working full time while supporting all aspects of my life, but I didn’t feel really adult like until I bought my house.
For me, realizing I had become a ‘grown up’ was when I was bummed out because I would not be able to attend a local city sponsored seminar on how get the most out of my new compost bin. 
That, and the fact that I have the vacuum cleaner bag model memorized and can easily pick new ones up when out grocery shopping.
Strangely, parenting my mother at age 10 and then getting kicked out of the house to live on my own at age 16 did little to make me feel very grown up at all.
Most of the time, though, I still feel quite young and am not sure I am entirely grown up at age 43. 
Interesting responses from everyone- great read. Thanks.
I’m pretty grey around the edges and still wonder what I’ll do when I’m a grown-up. One thing that really brought home that time was passing, though, was when my last blood relative (my sister) died.
When I learned to face down my insecurities. I was about 25. The moment you learn why you have to get all emotional about other people’s choices in life, you learn that you have some insecurities in yourself that you need to hash out.
If you face down all of your own fears and insecurities, you not only grow up and mature instantly…you also begin to all of a sudden see lots of people whom you thought were adults with brand new eyes. Some of them all of a sudden appear as insolent, fat spoiled toddlers, flopped on the ground, shouting and crying in immature frustration and rage. And you feel a bit embarrassed for them.
I was such a hot-tempered, insecure, immature brat as a child, that I really regret that my dad died before I ever really got to show him that I understand what he was trying to teach me all along.
When I broke my hip, and later started having arthritis and walking with a cane.
I’m 20 and this happened 2 years ago, hahaha.
I’m pretty much financially independent and I work 2 jobs, I do all the housework in my apartment, and I mother my 24-year-old boyfriend, but I’m still an undergrad and still work for pennies above minimum wage and still can’t drive (due to the car crash and loss of all driving skills that went with breaking my hip). I’m not sure where I fall because I have all the adult crap and my bosses and family still treat me like a kid.