Kudos for you, a 17 year old wanting to get involved, be productive, and earn some money.
I don't know if you have business aspirations, entrepreneurship, or similar, in your future. But, I would encourage you to approach your efforts as a business venture. This includes financial management, and building a good business relationship with your customers.
When somebody makes a post like this, it tells us that your financial management is probably not very sound. As others have pointed out, QuickBooks does this function very well. Any financial management software will prepare invoices, plus many, many other important functions. This includes bank statement reconciliation, records of expenses, records of inflows/outflows of cash, etc.
While I applaud your interest and efforts, I would encourage you to get off to a right start -- sound financial management. Getting off on this foot will not only help you manage your business, but teach you much about discipline and sound financial decisions (something badly lacking for start ups, and a major contributor to business failures).
Just my $0.02.
BTW, my suggestion would also be QuickBooks.