Kyles decision making was the correct decision to make .
He initially refrained from firing his gun , he walked away from the trouble and the mob and he even tried running away , he only used his gun when he was in danger , when his life was in danger , thats when he shot people .
Its nothing to do with age , many (older) people would have gone on a murderous rampage shooting as many people as they could
Kyle only used his gun when it was completely necessary , he behaved in a mature responsible way