Was William Jennings Bryan the youngest nominee of a party, winning or losing?
Yes, William Jennings Bryan was the youngest Presidential nominee of a major party. I’m not sure if any fringe nominees were younger, but it’ll be a tough record for anyone to break. Bryan was 36 years old the first time he was the Democratic nominee (he was nominated by the Dems in 1896, 1900, and 1908), so he was barely Constitutionally eligible to be even be President at the time. Bryan
As for VPs, John C. Breckinridge was 35 years old when he was elected Vice President in 1856 and turned 36 shortly before he was inaugurated. He’s the youngest President or Vice President to actually be elected or inaugurated. Breckinridge was also the Presidential nominee of the Southern Democrats in 1860 at the age of 39, so he’s also the second-youngest major party nominee for President. Breckinridge and Richard Nixon are the only people to win Presidential or Vice Presidential elections before their 40th birthday (although Nixon turned 40 just eleven days before he was inaugurated as Eisenhower’s Vice President in 1953).