Forty years ago, when Arlington resident Andrew Pang was 6, his friend Howard Wall brought him a souvenir from Louisiana, a robin’s-egg-blue 1976 dealer license plate. Pang, who was already interested in travel and geography, decided to buck the stamp-collecting trend and focus on license plates. “By the time I was 9 years old, I had one from every state.” The accountant and married father of two is still collecting, as well as selling and trading online. His treasures wallpaper the garage and fill a room in the basement.