1:36 a.m. EST March 7, 2014 06, 2014   If stock market gyrations seem more frequent this year, it could be due to the fact that the bull market, which turns 5 on March 9, is getting up in age.

The average bull since 1932 has lasted a little less than four years, says InvesTech Research. Using history as a guide, the current bull is graying around its horns.

So far in 2014, there have been nine days in which the Standard & Poor's 500 stock index finished up or down 1% or more, twice as many times as this time a year ago.

The "pickup in volatility is consistent with a maturing bull market," says Sam Stovall, chief equity strategist at S&P Capital IQ. Stovall's data show price swings are more dramatic in the early years of bull markets, level out in the middle years, then become wild again in a bull's later years.

In bull markets dating to 1949, the first year had an average of 60 trading days with gains or losses of 1% or more, followed by 38 in year two and 30 in year three. Volatility picks back up again in year four, and by year six, the number of 1% moves climbs back to 45.

Why?

Early in bulls, investors still have questions about the viability of the new bull. But as the rally matures, "and the memory of the pain inflicted by the prior bear market recedes, investors become conditioned again to buy the dips, thus triggering fewer 1% days," he says.

When aging bulls near six, the wild swings return as "investors again become wary of down days, realizing that bull markets don't last forever."