How much younger than 18? If it's within 2 years, you may be well served by spending the time building the software on your own - it's enough time that you can

How much younger than 18? If it's within 2 years, you may be well served by spending the time building the software on your own - it's enough time that you can learn the basics of web development (go Ruby on Rails!) and then you'll have gained something from the venture whether you've succeeded or not. I don't know what the incorporation laws are in the US with regards to age, but you may need to be 18 here as well.