Funny thing is, mostly negative things were listed above.
I'm going to be 39 very soon, and I wouldn't go back to my 20's for anything. Here's some advantages that I have that I didn't in my 20's:
No longer told "you'll understand when you're older" (and I do now!!)
You're no longer considered an idiot just because you're young.'
You get more respect in stores or business because people assume you have better credit and spending power. (and you do).
Kids. I know, I didn't understand it either when I was in my 20's. But I do now.
Enough money in the bank account to buy damn near anything you want on a whim.
Owning your own house.
Buying a pistol.
Not feeling like I should have my hair a particular way or dress a particular way because my friends do. In my day, you were supposed to have long hair. I look at my Senior picture in high school and college and just shake my head at what an idiot I looked like.
Insurance drops drastically at age 25.
Cops give you the benefit of a doubt.
Your parents respect you like an adult, not a child.
Not dependant on anyone for anything.
There's more, but like I said, I wouldn't go back 20 years for a million bucks unless I was able to know now what I didn't then.
Regards!
ps, my five year old is even worried about turning six. He doesn't want to grow up. I just remind him of all the things he'll get to do later that he can't now. Similar situation to yours, but not exactly the same.