You're in control of your faculties and capable of making investments now. But what might happen in the next 20 years? There's the risk of cognitive decline, which would make it harder for you to make sound financial decisions. Similarly, there's a risk you may fall prey to a swindler, which could happen regardless of your mental state.

"One big risk is trusting the wrong people -- or not trusting anyone," Mervine says.

To combat this, educate yourself now. Make sure you understand how the financial professionals in your life are paid and what incentives they might have to sell you products or ensure good results. Line up your trusted advisers now, while you're most able.

"You want to know how the incentives work, for you or against you," he says.