My colleague Chuck Saletta recently wrote an eye-opening article, "The Most Important Decade for Your Retirement." Chuck demonstrated how we can build a huge nest egg for retirement by saving aggressively in our 30s.

His numbers were tantalizing: You accumulate more than $300,000 by age 40, and then don't have to invest another dime. Your money grows merely at the market's historic annual average of 10% (which isn't guaranteed going forward, of course), and by age 60, you have $2.1 million. By age 70, more than $5.4 million!

Here's why those numbers are so exciting to me. I've learned, via the Fool's Rule Your Retirement service, that in order to make your nest egg last, you should conservatively plan to withdraw about 4% per year in retirement. With $2.1 million, that amounts to a generous $84,000 annual payout. And 4% of $5.4 million is a whopping $216,000 annual income, which surely dwarfs what most of us make these days (though in 40 years hence, assuming 2% inflation, $216,000 will have about $98,000 in purchasing power).

The bad news -- and the good
Unfortunately, there's one little catch for me, and probably for you: Our 30s are well behind us. All of a sudden, it may seem that Chuck's scenario is merely an if-only-I'd-done-things-differently dream.

Don't despair, Fool! Things aren't quite so bad. We might have missed out on our "most important decade," but odds are, we still have time to make more of our second-most-important decade -- our 40s.

Remember Chuck's results at age 60 and age 70? That $2.1 million and $5.4 million? Let's shuffle them around a little. He started the growth clock running with $300,000 at age 40. Change that 40 into a 50, and just tack on 10 years to the rest of the ages. All of a sudden, you're looking at $1.3 million at age 65, and $2.1 million at age 70. Those translate into 4% withdrawals of $52,000 and $80,000, respectively. Considering that you may also have Social Security, and perhaps some pension money to go along with that, things shouldn't seem so dire.

And better still ...
The situation can get even rosier. For one thing, as Chuck pointed out, you might be able to earn more than that 10% annual average by parking a portion of your nest egg in some carefully chosen stocks and mutual funds. Citigroup (NYSE:C) stock, for example, has averaged 16% gains over the past 20 years. Procter & Gamble (NYSE:PG) has earned 15%, while Boeing (NYSE:BA) has returned 14%.

Most mutual funds don't beat that 10% mark, but plenty have done so, and stand a good chance of continuing to do so. One of my holdings, for example, is the T. Rowe Price Media & Telecom (PRMTX) fund, which has averaged a 31% gain over the past three years and 35% over the past five years. (I don't expect such stratospheric returns to continue indefinitely, but the managers seem to be good at selecting strong performers.) Its top holdings recently included Amazon.com (NASDAQ:AMZN), Leap Wireless (NASDAQ:LEAP), Google (NASDAQ:GOOG), and XM Satellite Radio (NASDAQ:XMSR). It has a below-average expense ratio of 0.87% and no load.

If you're still worried
Of course, your situation may not be quite as promising. Perhaps you're already 50 years old, and your nest egg is a lot closer to $30,000 than $300,000. Perhaps you're actually in debt, rather than sitting on a small bundle earmarked for retirement. That's far from ideal, but there's still hope. Wherever you are now, you can position yourself for a better retirement tomorrow. Get out of debt, save aggressively, and invest effectively (but not recklessly).

The important thing is that you get a plan. In fact, research shows that one of the biggest predictors of retirement success is the presence of a plan -- but most Americans don't have one. To help you get started, I heartily recommend our Rule Your Retirement newsletter service.

Beginning this week, the Rule Your Retirement team will be taking subscribers through an eight-lesson "How to Plan the Perfect Retirement" online seminar. Reserve your seat for free by signing up for the Rule Your Retirement service. Get more details by clicking here.

Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article. Amazon.com is a Motley Fool Stock Advisor recommendation. The Motley Fool is Fools writing for Fools.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.