I'm 18 and not getting any younger, and this is how I know how...
1) You can no longer be bothered with the effort of tan or shaving your legs so you head out looking like a gorilla caught in a blizzard.
2) You've come to the realisation that the glory days of your boobs are over and there's no point trying to perk them up anymore because every 15 year old girl today looks like Pamela Anderson, so your pair don't even stand a chance at trying to attract some attention like they used to back in the good old 2012 days!
3) You realise a job actually is necessary for living after all...
4) You realise that instead of dealing with pointless drama its easier to just tell the people you don't like that you don't like them. Simples!
5) Your Nan was right, a coat really is the most important thing to bring on a night out after all!
6) Its hit you that the girl you hated so much and used to spend your days creeping on actually probably isn't the spawn of the devil after all and more than likely just liked that guy as much as you did (apart from Vanessa Hudgens, the hatred will never die).
7) You also go into a severe state of mortification when you look back on your list of past love interests. In reality, owning a guitar did not make him a musician...
8) When the time has come to bin your High School Musical magazines because they just take up too much space under your bed.
9) When you are struck by the realisation that your jeans don't have the ability to shrink by themselves and your body does actually have the ability to gain weight unlike it used to so its all downhill from here unless you cut down on kebabs.. Yep, life's a bitch.
10) When you realise that you actually have to decide what you want to do with your life and pop star/actress/princess/member of Totally Spies isn't really a logical option anymore because jobs aren't easy to come by during the Recession and your father isn't heir to any throne apart from the living room armchair when the cat finally moves!