Younger siblings are said to be more prone to risky behaviors than their elders.  This usually means stuff like drugs and sex, but now it means stealing bases:

For more than 90 percent of sibling pairs who had played in the major leagues throughout baseball’s long recorded history, including Joe and Dom DiMaggio and Cal and Billy Ripken, the younger brother (regardless of overall talent) tried to steal more often than his older brother.

Cap tap: Ron Siegel.