Do you think that if I buy this comforter while I'm 13, I will think it's childish by the time I'm 17 or 18?

It isn't that you will grow out of it, you will probably want an updated, fresh look again. We all choose to decorate our surroundings because we want a style that's fresh and new to us. If you do choose this beautiful comforter, you may want to change the paint color in your room later instead of buying another comforter. You can also update your room with a few small decorations to your room. That would change as you age. This is a very colorful comforter. If you choose to buy it, enjoy!