Yes they are.
Republicans? That map is not of a political party, it's showing regions in the USA.
But between their culture and their legislatures (check out what age people were getting married a mere century ago and who changed that), well, you do the math.
To date, the most conservative - Amish, Mennonites, hard core Mormon sects, folks up in Appalachia and other rural areas.... tend to have marriage ages far lower than anyone else. The closer you get to more densely populated areas, the north and west coasts... the higher the average marriage age.