"Grown Up"

When I think of my age and the fact that in only a few months I will be 27 I can't help but feel OLD. I don't know why. The number just sounds old to me. I wonder why it sounds so old when I myself don't even feel like a grown up yet. Is there ever a point when you feel "grown up"? What does it mean to be "grown up" anyway?
Dictionary.com defines "grown up" as reaching the age of maturity. So I've been "grown up" for almost 10 years and still I feel like a large child? At the age of 18 I purchased my first home. I then separated with the man I bought this home with and lived the life of working to survive and pay the mortgage. The years when I should have been out partying and exploring I spent working full time and watching $2.00 movies while I ate granola bars for dinner because I had a mortgage to pay for. When I was 22 I got married. I now live the typical adult life of working full time, paying the mortgage, coming home to my husband, cooking full course meals and planning for our future. Shouldn't I feel "grown up"???
I don't feel like I have missed out on anything. I did enough partying when I was a teenager to last my whole life. I've never enjoyed dating and venturing out on my own without careful planning just isn't who I am. The one thing I wish I did more of was travel however I don't believe this will make me feel "grown up".
I wonder if I am confusing this term for "complete?" There was a time shortly after my wedding when I felt my life was complete. I now believe as humans we are meant to constantly learn and grow and therefore we will never feel complete for long. Am I wrong? Are there people out there that feel completely whole, like they have it all and nothing could improve. Maybe I have to wait until I have had kids and they are "grown up" to finally feel like I have moved on from where I am now, a large inquisitive child with dreams of finding out what my true dreams really are? The only thing I really know for sure is that when my time comes to leave this world I want to have that feeling, that I have lived life, learned, experienced, "grown up" and feel complete.