I just turned 6-0. I liked turning thirty because then I knew my stepmother and other adults would HAVE to treat me like an adult; 21 wasn't quite old enough, old enough for me, but I felt adults still felt I wasn't really grown yet but at thirty, no one can deny it.
Each decade brings its own newness to it and can't really be compared to what came before or what is imagined after. Remember, you can't really know what it's like to be forty or even thirty-one, because that's future for you. I thought, especially when I was taking care of my stepmother when she got senile and I was in my late forties, that I knew what it was like to be old. When I got in my fifties, I realized I had had no idea whatsoever and I wake each day now astonished how ignorant I was at even fifty-five!
Think of it as an exciting new world and an adventure, not as getting old or regretting your youth; what you remember now has been well-filtered through time. Did you ever see "The Kid" with Bruce Willis? That's somewhat true I find. The problems you had in your "youth" teens and twenties will start to get fixed in your thirties and forties but it won't feel like it then :-)
I know the secret of all things now that I'm sixty

but I'm sixty and not thirty when I could have used a lot of those secrets!