The global economy may well improve in 2014, but that probability is already baked into a bull market that is past middle age, T. Rowe Price officials said today at a press conference. Consequently, they are urging investors to "be careful" going forward.

Bill Stromberg, the firm's head of equity, noted that the current bull market is up 164 percent in 4.7 years. That is very close to the average bull market since 1926, which lasts 57 months and appreciates 165 percent.

That said, Stromberg added that the bull market was "aging gracefully," with only a few signs of speculation and froth. Social media stocks are an obvious area of exuberance, and margin debt has climbed to somewhat worrisome levels.

While the global markets have dodged a host of potential calamities since the recession ended in 2009, eventually that will change. Stromberg said he expects the markets to experience some degree of "indigestion" when the Federal Reserve starts to taper or terminate its QE policies.

"Our sense is be careful and rebalance," he said. Most stocks are fairly valued or slightly overvalued.

Alan Levenson, T. Rowe Price's chief economist, sees a number of positive factors that could cause economic growth to accelerate in 2014. "The fiscal drag is set to ease substantially" next year, he said.

Business capital spending, which has risen only 2.7 percent over the last 12 months, should increase by 7 percent next year, Levenson said. Consumer spending was curbed earlier this year by tax increases that took effect this past January. No new tax increases are scheduled to occur in 2014.

Contrary to popular wisdom, most of the new jobs created in recent years have been full-time, not part-time, jobs, Levenson added. Still there is a lot of slack remaining in the economy.

John Linehan, head of U.S. equity, said he would not be surprised if there were a correction of 5 percent to 15 percent next year, even though such a correction would not be accompanied by a recession. "We've had no correction [of any significance] for quite some time," Linehan observed.

On a positive note, Linehan thinks the U.S. manufacturing renaissance is a story that could have legs. Recently, an executive at a copper company told him the total cost of hiring a truck driver was $70,000 a year in Chile and only $60,000 a year in the U.S.