Investing in stocks to be a millionaire for 22 years. Talk about negative cash flow!

[Jeff S.]

If you can only invest $1,000 every month and have nothing in savings. If he earns a 10% annual rate of return (compounded quarterly) in a portfolio created by a robo advisor, Investor A will need 22 years and seven months to become a millionaire.

People gripe about negative cash flow but with this plan you probably can't touch it until 59 anyway. A tough road. How about leveraging then sticking that grand toward debt?