If you're a man in your early 20s, consider growing tomatoes. 

Don't hesitate to take on debt if necessary. 

Invest $50 to purchase 10 tomato plants. 

After six months, you'll harvest around 250 tomatoes. 

Use those to seed 250 new plants. 

In another six months, you'll have approximately 6,250 plants. 

Plant them again. 

After the next six months, you could yield around 156,000 tomatoes. 

Replant those as well. 

In six more months, you might produce about 3.9 million tomatoes. 

You can sell each one for $1.