Age is just a number. With the stock market attaining the crown of the longest-running bull market in modern financial history, investors should not fret over the milestone but should focus on the solid underpinnings driving the run. The current bull market rally, which started March 9, 2009, became the longest one on record since World War II on Wednesday by avoiding a 20 percent or more decline, according to S&P Dow Jones Indices. The market has risen more than 300 percent since its low nine years ago. On Tuesday, it tied the rally from 1990 to early 2000, which totaled 3,452 days, and hit a record high. (There's only one caveat: if the stock market failed to rise above Tuesday's record and dropped 20 percent from here, then it would be a tie. In early trading Tuesday, the S&P 500 was sitting just below that record and flat for the day.)

Belpointe chief strategist David Nelson warned investors to ignore the skeptics who may use the milestone as a reason to get out of the U.S. stock market. "The data still points to U.S. equity markets as being the better asset class. Look around the world. We're the best game in town," he wrote in an email Monday. "If someone calls telling you to take money out of the U.S. and put it in emerging markets because they are cheap, HANG UP. Dead money for 12 years. Cheap for a reason." One Wall Street veteran explained the rally's length is unimportant, and what matters for the market is the economy's strong growth. "Bull markets don't die of old age. What kills them is recessions," Yardeni Research's Ed Yardeni said Monday on his website. "The earnings picture has been so bright. … I think we're going to have a long expansion. I think the bull market continues." Yardeni reaffirmed his 3,100 year-end target for the S&P 500, representing 9 percent upside to Monday's close. In similar fashion, J.P. Morgan Chase CEO Jamie Dimon agreed the state of the economy is the main driver for the market. He said earlier this month that the current bull market could "actually go for two or three more years."

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