USFstudent...
I'm totally feeling you!!! I had the same thoughts and feelings at each of those ages also, right up to 21. 22 wasn't so bad, but when I turned 23 and could no longer be under my parents medical/dental insurance it through me right back into my slump. I'm turning 24 in April. I feel that I am finally coming out of this midlife crisis that I've been going through for the last four years.
I have always fussed over what age I was at only to discover another year has passed me by. So, I have learned/am learning to enjoy everyday and embrace the age I am at, since I am just going to get older