Fidelity found boomer millionaires, who are 49 years old and older, are more likely to stick with the same old investment strategy. Four out of 10 boomer millionaires did not add any asset classes in the past year. Meanwhile Gen X and Gen Y millionaires, who are 48 years old and younger, are more willing to make changes and add more complex investments, such as foreign currency, international individual securities, venture capital and derivatives, to their portfolios.
(Read more: Retiring with more: Don't wing it on your 401(k))
Still, careful planning comes first. It is an essential building block at any age.
That's what younger millionaires do—even though retirement may be decades away. "Because they're planning, they're diversifying, they're thinking long-term," Glassman said. "And that's what's allowing them to take additional risk in places where it's prudent."
—By CNBC's Sharon Epperson. Follow her on Twitter @sharon_epperson. See more Money News from The TODAY Show at ourFacebook and Twitter pages.