Why do we want to "grow up" so fast?

It's a weird feeling to be young, and want children. Most people think you are crazy, and need to enjoy your youth. While I do want to get married, and have kids. I understand why people put it off. It's nice to not have a million things to worry about. Once you have kids it's a luxury to go to the store whenever you want, and to be  spontaneous. As much as I want to get married and have kids young I know I need to enjoy the things in my life now. I need to take this time in my life to save money, maybe pursue an online business, pay off my debt, and go back to school to finish my degree. So later in life I want to be prepared financially, and hopefully better mentally to have the life I want.