More than a decade ago, Clark put up a chart (see below) in one of his books that showed how a teenager who starts saving at 15 and puts aside $2,000 for 7 years will have more than $1 million at retirement.

Over the years, people have challenged this claim and the methodology behind the numbers. So now personal finance columnist Gail MarksJarvis at The Chicago Tribune has run the numbers and corroborates what Clark has always said.

Her figures differ only trivially from those Clark had presented. According to MarksJarvis, if a 16 year old saves $2,000 annually for six years into a Roth IRA account and stops at age 21, they'll have $1 million when they turn 65.

This assumes a 9.4 percent average gain annually, which has been the average return on the stock market since 1926, according to The Chicago Tribune article.

Saving money early -- not even often, just early -- will still ultimately lead you to $1 million in wealth at the time of retirement. If you keep saving after your 21st birthday, you'd end up with somewhere between $2 and $3 million at retirement.

The key always is to save early. That's the hardest part. Most people don't start thinking about saving until their 40th birthday. But if you start early, it makes a big, big difference down the road. See below: