What can I do now to start a software business (if 17 years old or more)
You just need to be more clear about your goal than software only.
Software has large setup of work and goal to purse for personal (public/ individuals) and business as well.
You need to know how to start the business first,
Requirements of business,
Your mission to start it (you must know that),
What's your role in it?
List the available resources and also which is unavailable for business.
Make a plan and procedure to run it,
Don’t forget to have a better team with you,
Think which better thing you are adding,
How to execute the plan,
Where would you like to reach plan within years,
How it will be helpful for humans and in solving issues,
Learn how to execute the plan if initial plan fails,
Don’t think much about issue rather start with passion.
There are may thing which you will learn while working so you don't need to worry about all consequences.
You will have good success if you have better vision and service.
Source: Ankit (Q&A)