By Dan Weil Stocks have slumped 21% this year. Keep two basic factors in mind: your age and your risk tolerance. Stocks have slumped this year, with the S&P 500 dropping 21% so far amid soaring interest rates and sluggish economic growth. The market could easily fall further as the Federal Reserve continues to raise interest rates to combat inflation. So what’s an investor to do? Keep two basic factors in mind: your age and your risk tolerance. For people under 30 or 40, a strong case for devoting 80% to 100% of your portfolio to stocks can be made. That’s because they outperform bonds over th…