Nearly a third of retirees are playing chicken with one of the steepest tax penalties out there — and they are running out of time. IRS rules on so-called required minimum distributions generally kick in once you reach age 70½. For 401(k)s and other defined contribution plans, it's either when you turn 70½. or you retire, whichever is later. If you've inherited an IRA, you might also be subject to RMDs, even if your own retirement is years away. How much you need to take is usually based on the account balance at the end of the previous year, and...