According to this story, U.S. Senator Rand Paul was asked by a member of the audience if he would support the Libertarian Party nominee in 2016 if he doesn’t get the Republican nomination. Paul said that he expected to support the Republican nominee and said he had never endorsed a Libertarian Party nominee. But the questioner then reminded him that he had indeed endorsed Ron Paul, the Libertarian presidential nominee in 1988, and Paul at that point acknowledged this point.
Rand Paul was 25 in 1988. He attended the Seattle national convention of the Libertarian Party (held in September 1987) and worked on his father’s presidential campaign that year.