According to the U.S. Census Bureau, Provo, UT was the youngest city in America in 2010 among places with more than 100,000 people. Oldest cities in America.

Place	Median age (years)
Provo, UT	23.3
Gainesville, FL	24.9
Athens-Clarke County unified government, GA	25.9
Tallahassee, FL	26.1
Columbia, MO	26.8
Killeen, TX	27.1
Denton, TX	27.1
Ann Arbor, MI	27.8
Laredo, TX	27.9
Tempe, AZ	28.1