I get that feeling every so often, and it freaks me out, too. I have felt like I was in my early to mid 20s since I was like 15 or 16. I still feeel pretty much the same way I did back then, with a few changes, mainly in wisdom. I still feel and think like I am 26, even though I just turned 39, which blows my mind in itself. I wish someone would have told me when I was in high school that this is the way you will always think of yourself; it would have done wonders to my outlook and insight on other people's feelings.
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I was always told that there is safety in numbers, so I majored in math.
"Lunch...is on Millie" - Ace Rimmer