Never ever do it with just money in mind. Remember, to make any money you must compete with wholesale. That means fish 1/3 or a 1/4 of what you see in shops, and the local market is only so big. Maybe an LFS will take them from you but it'd be difficult to make it profitable.
To open a fish store I'd say start studying some marketing, business and everything you'll need. If you know that securing capital will be easier and it could be better to start
Believe me, if you're 14 it'd be better to just sit and enjoy the hobby! I'm a tad older and I just sell odds and ends (usually plants) to help save for this or that. Too much business and it isn't as much fun. Good luck in your ventures