Yes, it is fun, whatever "it" is. Oh wait, "it" is growing up!
This song means that you may be at the "top of the food chain" and be all cool while you are a child, but when you "go out into the real world" with no one at your back, "don't go crying to your mama" because it will be hard! Most children think that the adults have lives with SO many privileges, but they don't realize how difficult their parents' lives actually are. Also, the "rebels" think that they don't have to listen to anyone, and they like being "free to do what they want"... Until they realize that with freedom, there is a price. Working, receiving money to support yourself, and supporting a possible family... That is what adulthood is about.
To those popular people who think that you can do WHATEVER you want, whether it's bullying (burning bridges) or failing school (almost guaranteeing a poor future), watch out. You may have all the fun in the world by doing these things right now, but when you reach adulthood, ultimately, popularity doesn't help you find an income of money. Neither will your looks help you when you are begging on the streets, because "you're not the big fish in the pond no more. You are what they're feeding on." When no one's at your back, what are you going to do? Ask your "so many friends" for help? What if your "friends" aren't in the area where you are? What if they aren't even your friends? The world won't always assist you when you need it to, like those people that you bullied (that are probably quite successful right now) when you, well, bullied them. Because "if it don't hurt now then just wait, just wait a while" and when it does hurt, it's going to hurt A LOT. Life is easy when you're pulling the strings on your tiny stage, but when you enter the big stage of life, nothing will be easy, because other people are pulling the strings. Earth to you popular people who think that money grows on trees and that life as an adult will be easy; there are 7 billion, and counting, more people in the world, and they won't orbit around your life to help just you. You have to take responsibility for what you do, and don't expect anyone else to help you while you're at it. Those bridges you burned? Fix them. That lack of education? Learn what you can while you still could change your fate.
Ain't It Fun?