It's funny how, at least in my case, when you get to a certain age, people mistaking you for being younger, kind of feels like a compliment. We spend our entire childhood and teenage years trying to appear older, wiser, more mature than we are, and then one day, when you reach a certain age, you're no longer insulted when people say you look younger. What, to you, once meant "childish, underdeveloped and immature", suddenly has a whole new meaning: beautiful.
When you're seventeen you want people to think you're twenty one. But when you're twenty six, at least in my case, you don't mind people thinking you're seventeen.
I get mistaken a lot. Especially by cashiers. Whenever I'm buying alcohol or tobacco, they ask me for ID to make sure I'm at least eighteen years old. Even when I'm buying energy drinks, they sometimes ask me to show them my ID, even though you can legally buy energy drinks from the day you turn fourteen. When I willingly show them my visa, which has my date of birth printed on it, they give it back with a slightly embarrassed look on their face. As if they just realized they insulted me. "Oh.. You've been old enough for a long time", a female cashier said to me the other day. I couldn't help but smile. To me, being mistaken for being younger is not a bad thing. It just means I have no visible signs of aging on my face. Honestly, it's nice to know my weird habit of using suncreen every day and keeping out of the sun is paying off.
When I was a teenager people used to mock me for looking younger, but guess who's laughing now, bitches!
(Also, looking younger might just earn you cheaper tickets on the bus / train / zoo / anywhere, and the clothes in the childrens section are usually cheaper. So there's that.)