Katniss, the protagonist from The Hunger Games, is describing the electrified fences, in chapter one (page 5), when she discusses the events which caused her father's death. Katniss, five years after her father's death, still awakes from dreams screaming because of the circumstances.
Katniss "was eleven then," as she recalls her father's death. She is recalling the fact that her father, before he was "blown to bits in a mine explosion," taught her how to find food in the woods where the animals which she hunts for are able to roam freely. The electrified fences are supposed to keep out the "flesh-eaters," which they succeed at doing.
Therefore, readers are given the fact that Katniss was eleven (11) when her father died five years ago. The novel takes place when Katniss is sixteen (16).
At the time Katniss was 11 years old and she remembers that her father was blown to bits in a mine explosion. Sometimes she still awakes from nightmares that relate to the past. Her father practically taught her everything he knew about hunting.
Katniss was 12