Standing at about 4 feet tall, with a waist no larger than the hydrant next to him, 7-year-old Aaron Oliver doesn’t look like the average firefighter. Then again, Wednesday was no average day for the diminutive first-grader. While his peers were sitting in school, Aaron was more than two stories in the air, wielding a spraying hose; he was behind the wheel of a fire engine, radioing to dispatch; and he was checking safety gear, ensuring its availability at a moment’s notice.