I rarely spend much time on one game any more, I maybe have a dozen RPGs with 50-100 hours each on them, but doing some rough calculations I reckon I spent between 1 and 2 years playing Civilization as a kid. All day, every day, every school holiday for about 10 years. The fact that it was on my Amiga and took ages to work out the AI's moves helped clock up the time, though.