Everything we know about becoming an adult has changed. Adulthood is really about your brain, the culture you live in, and how you function. Neurologically speaking, your brain doesn't finish developing until your mid-twenties. That's when the prefrontal cortex, the part of your brain that plans and controls emotion, is good to go. From a functional side of things, it's more about staying healthy, defining your identity, becoming financially independent, finishing your education ... but that's a lot of stuff. The experience is different for everyone. It's like a video game. Eventually, your character is going to beat the level, but everyone gets to the end their own way. The maturity of becoming an adult is understanding your strengths and weaknesses.