Bristol Palin, the 18-year-old daughter of Alaska’s Gov. Sarah Palin, has broken off her engagement to the father of her 2-month-old son. Palin and 19-year-old hockey player Levi Johnston became engaged after the pregnancy was revealed during Sarah Palin’s vice presidential campaign. Johnston this week said he’d like to marry Palin eventually, after he grows up a bit. “It’s just me not being mature enough, or something,” he said.