Turning 18 is a highlighting point in a teenagers life. I mean, you're an adult now, you can vote, you can legally be on your own, you could get married! So, why do people think it's so weird to be mature?
It's okay to want to stay home from a party and just relax, even if it's Friday night. Growing up to fast isn't necessarily a bad thing, it just means you know what you want in life. Some 18-year-olds know what they want for a career while others are more concerned about who's being the DD for Saturday's party. Both are okay!
This is usually the time in a teenagers life to experience the world now that they have the freedom to. Some of us don't need this time to explore, we already know what we want. Stop feeling bad for not wanting to go to that frat party or skip class that day to go to the beach. Forcing yourself to be someone you're not is never the right choice.
Your outfit choice can really show how mature you are. Some of us are content with shopping at Banana Republic or The Loft because their clothes are cute and professional. Others still shop at Charlotte Russe and Forever 21 looking for crop tops and concert tees. You should always wear what makes you comfortable and not what other people think you should wear.
Surround yourself with older friends because they can help you figure out what you want in life. You can base your goals off of them and see if you want to be like them or the complete opposite. Older people can help you be more mature if that is what you're looking for in life. Once the "party stage" is over you might want to move on and start your life.
Being mature at 18 is never a bad thing, you're only helping yourself for when you need to find a real career. You may feel like you missed out on the parties or the social aspect of being a teenager but even when you're older you can still have fun with your friends. I can promise you no party will be worth the idea of ruining your potential career. Be yourself and don't feel like you need to amount to anyone standards other than your own.