My home had many aquaria in it before I was born, so they have always been around (my grandfather began keeping aquaria in the early 1930's, and my father in the 1950's, so aquariums were a standard part of our life)...but I received the first tank of my very own when I was 4. Although I was young, since my father had always made me a part of tank maintenance, I was quite capable of taking care of an aquarium on my own.
It was a slate-bottomed, steel-framed 10 gallon tank with a stainless-steel hood, occupied by three Corydoras julii, four fancy guppies, four neon tetra, and 3 silver hatchetfish. Filtration was via a small, plastic, air-driven box filter in the corner....heat was from a hang-on tank submersible glass heater (which was never on during the day, as the incandescent tube under the steel hood warmed the tank pretty good).