Here's a thought- depending on where you live (like a neighborhood with a lot of homes), there might very well be people/neighbors in your area that have loads of dull knives in their kitchens. Everyone has kitchen knives, but not everyone knows how to sharpen them, or has the tools to do so. Instead, they just live with dull knives.
So here's an idea- Print up a bunch of flyers, something like "Knife Sharpening. Low prices. Will pick up and deliver. Satisfaction guaranteed", etc, etc. Provide your name, your contact info, and your prices. Then go around your neighborhood and distribute the flyers. But DON'T knock on peoples doors, people generally hate that (I know I do), just stick the flyers in their screen doors or somewhere they will see it.
If you see anyone out in front of their house, Smile and say "Hello, excuse me, can I hand you this flyer for my knife sharpening service". And if they say "No" or "No thanks", just smile, say "Have a nice day", and move on to the next house.
If you are a Boy Scout, wear your uniform. I think people would be more receptive to a teenager in a scout uniform.
You would have to create a simple price list. You certainly don't want to try and charge $10 for a single kitchen knife. Bulk discounts would also be a good idea.
And don't get into details like "What steel are your knives made of", or "What bevel angle do you want", because most people won't know what you are talking about, and they might get turned off. Just put a sharp edge on their knives and they will be happy.
Your biggest obstacle in starting your own sharpening business is your age. While there are many capable and responsible 14 year olds, people might be reluctant to hand over their knives to one they don't know.
I could go on and on about starting a knife sharpening service, but this is enough for now. Good luck to you.