It's not a valid reason. In fact, it's kind of insulting to ask for free money for the pleasure of something totally unnecessary.
Is starting a fundraiser online to raise money for a concert you want to go to really badly a valid reason? I don't have any money or way of earning it and my family is very low on financial give outs.
You don't need a fundraiser. You need to work to earn your money Underage, you say? Well, what's wrong with mowing a lawn, raking leaves, cleaning out your neighbor's garage? The possibilities are endless. Tutor someone that's struggling in math, take photographs and sell them, etc.
The sooner you connect work with money, the easier your life will be. Don't expect money for doing nothing. Learn to work for what you want.
I remember a 12 to 14 year old whom I had never seen before asking me to give him 50 cents for something.
I told him "No," but that I admired him for asking.
My comment impressed him very much. I had confirmed his assertiveness and judged it to be a good thing.
Learn to validate what you do whether or not other people agree with you.
The fact that you considered getting input from others before you act indicates that you are capable of properly evaluating your own reasons for action in life.