In your 20s, you can invest dribs and drabs in the stock market and, through the wonders of compounding, become a millionaire by the time you retire.
Unfortunately, that magic trick no longer works once you turn 70.
"The biggest challenge a 70-year-old has in getting rich is, obviously, time," Tilp says. "The younger you start, the easier it is."
To become rich after 70, you'll need to invest a lot of money every month, and pray for good returns.
James Twining, founder of Financial Plan in Bellingham, Washington, has run the numbers. He figures a 70-year-old starting with nothing would need to invest $2,393 a month at an annually compounded rate of 10 percent per year to earn a cool $1 million by age 85.
"The equity markets have, indeed, returned an average of 10 percent per year since 1926," he says. "So, it is not unreasonable."
Older investors wishing to get rich sooner may be tempted to gamble on high-stakes stock picks. But such a strategy actually decreases the odds of success, Twining says.
"The biggest challenge will be to resist the temptation to take risks by concentrating the portfolio -- attempting to pick winners, or to time the market," he says.