Jennings grew up in Phoenix, Maryland. As a child he was an active 4-Her, raising market lambs and cattle and showing them at various fairs including the Maryland State Fair. At the age of sixteen he joined the Jacksonville Volunteer Fire Company Station 47, where he was a firefighter and emergency medical technician. He eventually became a lieutenant before serving on the board of directors. In 1994,a he, and several other firefighters from Maryland, were sent to Idaho to fight wildfires that were raging due to extreme drought. They received recognition from Maryland Governor William Donald Schaefer for their actions.