-When you spend your "fun" money on things like blenders, new shower curtains, and high-quality baking supplies.
-When each birthday is just a birthday and not a milestone (14=get a summer job, 15=driver's permit, 16=drive; 17=movies, 18=smoke, gamble, sign your own consent forms, 19=last year of teenhood, 20=not a teen!, 21=drink etc & fully legal adult; 22+ = ?)
-you can buy ANYTHING YOU WANT at garage sales because a) you have more than $5 to your name, and b) Mom's not there to say "your room is too messy, you don't need any more stuff!"
-you are so used to waking up at the same time every day during any season that you wake up without your alarm clock.
-you realize you are now allowed to get a pet monkey if you wanted to!
-"kids these days" don't remember what it was like before cell phones, mp3 players, free email accounts, gps navigation systems, etc. You remember using portable tape players and thought a portable CD player was so cool except that it skipped if you jogged; had to get out of a broken-down car and walk to the nearest landline phone, had only 1 email account because it cost an annual fee, and you know how to read a roadmap. (do I sound old? I'm only 23...)