South_agency / Getty Images If you contribute to your 401(k) in your early 20s, you're taking advantage one of your greatest assets: time. The more time your money is in the market, the more time it has to grow and compound. Key Takeaways Starting a 401(k) early gives compound interest more time to grow your savings. Employer matching is essentially free money that accelerates long-term returns. To choose between a traditional 401(k) and a Roth 401(k), decide when you want to pay taxes—either now (ge ...