Those suffering from diabetes do so because his or her body cannot produce or respond to insulin in the way that most bodies can. Over time, diabetes can result in numerous other health problems that might keep somebody from lving a normal life.
Jimmy has a lot to achieve if he wants to become a pilot in the air force. While the necessary steps have changed over time, if Jimmy wanted to become a pilot in mor emodern times he would need to complete a bachelor's degree program. He would then need to earn commission as an officer. There are numerous tests and training programs that would follow. It's definitely not something Jimmy could decide to do on a whim.