Reuters/AFP Copyright: Reuters/AFP

Bernie Sanders and Pete Buttigieg, the two current frontrunners, have an age difference of four decades - Sanders is more than double his rival's age.

In his speech in the past hour, Buttigieg mentioned admiring Sanders while he was in high school.

Buttigieg was born in 1982. At that time, Sanders was the mayor of Burlington, Vermont - a post he'd hold from 1981 to 1989.

When Buttigieg was graduating high school at age 18 in 2000, Sanders was a member of the US House of Representatives.

That same year, Buttigieg won an award for writing an essay about Bernie Sanders where he called him an "outstanding and inspiring example" of integrity.

"In a climate where even liberalism is considered radical, and Socialism is immediately and perhaps willfully confused with Communism, a politician dares to call himself a socialist? He does indeed."

Buttigieg became South Bend, Indiana, mayor in 2012 - at which point Sanders was in his second term as senator.