"He is a small man with blonde hair and bronze skin. Even though he just celebrated his 48th birthday, he still looks like he's in his twenties; way too young to be a mayor."
-Maika Sheert talking about Mayor de Solenill
This Mayor was the mayor of District 1. He is mentioned during the 66th Mentoring, so he could've been the mayor, even during the 74th and 75th Games, and possibly the Second Rebellion. He was born during the 19th Games.
However, this can't be confirmed yet. He is said to be a small man with blonde hair and bronze skin. Even though he just celebrated his 48th birthday at the time of The 67th Hunger Games, he still looked like he was in his twenties; way too young to be a mayor.