A 25-year-old who invests $500/month for 10 years and then stops contributes $60,000 total. At 7% average annual return, by age 65 they'll have approximately $1.1 million.

A 35-year-old who invests $500/month for 30 years contributes $180,000 total. At the same 7% return, by age 65 they'll have approximately $567,000.

The person who invested for one-third as long and contributed one-third as much ends up with nearly double the money. This is the compound interest table that changes how people think about starting early.

The practical implication is not that you should stop contributing at 35 — contribute continuously for the best outcome. The point is that the first decade of contributions is the most valuable decade, and delaying it is the most expensive financial mistake most young people make without realizing it.