Your are your 'selfish' years. It's a decade to immerse yourself in every single thing possible. Be selfish with your time and all the aspects of you. Tinker with shit, travel, explore, love a lot, love a little and never touch the ground.
"The true mark of maturity is when somebody hurts you and you try to understand their situation instead of trying to hurt them back." // (I don't want to label what "the true mark of maturity" is, but this idea of empathy vs revenge is important to me.
"Maturity comes when you stop making excuses and start making changes." When you stop making excuses about why you lied, mistreated someone or abused someone and accept your responsibility, positive change will happen.