Quick Verdict
Mostly myth. The longer you wait, the more you may need to save later.
Why People Believe It
In your twenties and thirties, retirement can feel very far away. Rent, loans, children and everyday expenses seem much more urgent.
Reality Check
Starting earlier gives savings more time to grow. If you begin at forty rather than twenty-five, you may need to set aside a much larger amount every month to reach the same goal. Of course, not everyone can save much when they are young, and investment growth is never guaranteed. It is also not too late to begin in your forties or later. The point is that putting it off gives you fewer years to work with.
A Better Rule
Start planning when you reasonably can, even if you begin with a small amount. Increase your savings as your income and circumstances allow.