Hey :)
Personally, I've had very similar experiences to yours. My social anxiety is extremely severe (debilitating during my Junior year in HS, but really its been a part of my life since I can remember) and it is coupled with dysthymic disorder (depression that doesn't really go away, just gets worse or better at different times). After my Junior year, I knew that I couldn't go back to my HS and be able to have a good, fun, low(er) anxiety time. My parents and I decided to switch me to a new HS my Senior year (along with my younger sister and younger brother). I ended up switching to another small private school (a bit bigger than my previous school, but still pretty small).
About 2 months before my Senior year started, I had this revelation. It was like I could finally see myself and where my life was headed. I decided to develop a motto that I could use to remind me to not let my disorder(s) rule my life/ (Although they obviously still affect me - they don't DICTATE what I do anymore.) The motto I came up with is: "Do not simply survive. THRIVE." Idk if you can relate, but I had been doing that - surviving - for the majority of my life. I didn't get attached, emotionally inbvolved, or participate in the "normal" things my peers did. I went through the motions of living without really doing anything! I would wake up, get dressed, sit through all my classes, come home and do homework, eat dinner, and spend the rest of the night with the TV, reading, or art. (Not that I don't still do these things lol, but I've been able to incorporate so much more activity, energy, and opportunities into my life!)
I bought a picture frame, printed out my motto on the computer and decorated it, and framed it in my bedroom where I would see it about ten times a day. It has gotten to the point where before I make a decision (ie. staying home alone or going to the movies with friends) I think of my phrase and decide: If I didn't have anxiety, what would I want to do? How do I want to look back on my weekends of HS/college or just my years in general?
Now, even though my anxiety still keeps me a little different from my peers, I have finally been out to the movies with friends, been to sporting events (and actually enjoyed them!), gone shopping with my sisters just for fun, been able to ask for what I want/need (whereas before I would suffer through, no matter how easily the situation could be resolved. Now I can, if I want, take a stand and say, hey, this is what I want! Not that I always make people do it, but I have finally found my voice!).
The biggest accomplishment (in my eyes) happened a few weeks before Sr year (about 2 months after I developed my slogan). I didn't know anyone in my new class but the school had decided to have a white-water rafting trip for all the seniors. Initially, my anxiety took hold and I told my mom I wasn't going to do it (A whole new experience, in a new place, with A LOT of complete strangers?? No way! lol). My mom said OK, but suggested I think about it for a few days. That night, I went up to my bedroom and there it was - Do not simply survive. THRIVE. - staring right at me. I suddenly thought, when are you ever going to get another chance to do this? who cares if it's new people, you're going to spend the next year with them so you might as well get to know them before school starts! I turned around, found my mom downstairs and told her that I changed my mind-I was going to go on the trip after all. Although it was a really stressful time at first, eventually I warmed up to the new people, had a blast on the rapids, and made some friendships that lasted throughout my school year (and now into my first year of college).
This was a major breakthrough in my problem of being scared to grow up and just (albeit it sounds ridiculous) "taking the time to live in the moment."
(My mom would later confess, after several months had passed, that she was terrified to let me go! She knew my anxiety and problem with new people - and I can't swim well, lol, so I think the water scared her too. She had been so afraid that I would regret my decision or have a panic attack while away that she had actually talked to my counselor about it. He ended up telling her that, yes, it was a scary thing, but it was a major deal that I was willing to try a new thing, be adventurous, and do all that with strangers! About the panic attack, he told her, even if I did have one - I had been having them for all my life! I knew what to do, how to handle it, and frankly, he told her, no one has ever died from a panic attack! She admitted to me that it was so hard to let me go off by myself, but she knew it would help me in the future if I could do this through all my anxieties.) Her and I still joke about this incident!
But back to your topic, I would say, YES! A lot of people are scared to grow up. Everything's so unpredictable and there are so many new things that come with "growing up." I have to constantly remind myself that althoughthis is true, growing up also presents SOOO many more opportunities for fun with so many new, exciting, and different people! (Which, I've learned, CAN be a good thing! :)