American retirees are investing more like 30-year-olds. Rather than follow the conventional wisdom to protect their nest eggs by shifting their investments from stocks to bonds as they age, many are rolling the dice. Nearly half of Vanguard 401(k) investors actively managing their money and over age 55 held more than 70% of their portfolios in stocks. In 2011, 38% did so. At Fidelity Investments, nearly four in 10 investors ages 65 to 69 hold about two-thirds or more of their portfolios in stocks. And it isn’t just baby boomers. In taxable brokerage accounts at Vanguard, one-fifth of investors 85 or older have nearly all their money in stocks, up from 16% in 2012. The same is true of almost a quarter of those ages 75 to 84. Having significant exposure to stocks later in life can be risky, advisers and economists say, if only because if the market were to tumble, retirees needing cash may have no choice but to sell their shares at bargain prices. Many changes over the ...