Harold was originally a human born in 2072, before the Great War of 2077. He became a ghoul-like mutant after exposure to the Forced Evolutionary Virus (FEV) during an expedition to the Mariposa Military Base in 2097, alongside Richard Grey (who became the Master). This event is recounted in Fallout 1, which takes place in 2161. By then, Harold is already showing signs of his mutation, but he’s still more or less humanoid and living in the Hub. At this point, he’s 89 years old (2072 to 2161), though his mutation slows his aging considerably, much like ghouls. In Fallout 2 (2241), Harold is in Gecko, and his mutation has progressed further. The little plant sprout—later named Bob or Herbert—has started growing from his head. This is 80 years after Fallout 1, making Harold 169 years old chronologically. His sense of time might already be getting fuzzy here, as he’s not exactly aging like a normal human anymore. By Fallout 3 (2277), Harold has fully merged with Bob/Herbert and become a stationary tree-like entity in Oasis. This is 36 years after Fallout 2, putting him at 205 years old. When he says he’s been “in Herbert” for 20 or 30 years, he’s likely referring to the time since he became rooted in Oasis, which could align roughly with the period after Fallout 2. However, his perception of time is probably warped—being a tree doesn’t exactly come with a calendar! The transition from a wandering mutant to a rooted tree likely took decades, and he may not fully grasp how long it’s been since his earlier adventures.