If you're 23 years old and deposit $3,000 per year (that's only $250 each month!) in a Roth IRA earning an 8% average annual return, you will have saved $985,749 by the time you are 65 years old due to the power of compounding. If you make a few extra contributions, it's clear that a $1 million goal is well within reach. Also keep in mind that this is mostly interest — your $3,000 contributions only add up to $126,000.
Now, suppose that you wait an additional 10 years to start contributing. You have a better job and you know you've lost some time, so you contribute $5,000 per year. You get the same 8% return and you aim to retire at 65. When you reach age 65, you will have saved $724,753. That's still a sizeable fund, but you had to contribute $160,000 just to get there — and it's nowhere near the $985,749 you could've had for paying much less.