More realistically, if you get a 5% return on your investments (or ~2% after inflation), in 43 years you'd have $14,663,123.

I'm lucky enough to be making ~$400k at 30. At 21, I was lucky enough to be making $65k. Virtually no one starts off making $500k. Even if you start at the top 1% of income earners and stay there your entire life, live relatively frugally, never have kids, never take a break from work, and invest well -- even then, you're still unlikely to accrue $10M in wealth.