A Closer Look at Income Inequality - Andrew Syrios - Mises Daily: "say everyone in the country made the same income, but got a promotion each decade. They start at $20,000/year in their 20s, then they go to $30,000/year in their 30s, etc. In addition, they save 5 percent of their income each year and make no return on their savings. To make things simpler, we’ll assume there is the same number of people in each age bracket."
Then those over 60 would have 30% of income even though they represent only 20% of wage earners.