It's pretty obvious to me, this song is encouraging insecure, young people to just be themselves and not worry so much about what other people think, because there will come a day when it's even more inappropriate for them to act and be as they like - that is, when they grow up and become adults. Adults are expected to act in a certain way and look presentable at all times in order to be accepted by society.
It could be that there is some sort of sarcasm in it as well...
It's pretty obvious to me, this song is encouraging insecure, young people to just be themselves and not worry so much about what other people think, because there will come a day when it's even more inappropriate for them to act and be as they like - that is, when they grow up and become adults. Adults are expected to act in a certain way and look presentable at all times in order to be accepted by society.
It could be that there is some sort of sarcasm in it as well...