12 – 16 years
This is NOT a step-by-step guide, so please don’t use it as such. Attempting to destroy the world will always get you into a lot of trouble (unless you succeed, I suppose).
It does, however, describe a whole range of possible apocalypses, together with their likelihood of happening, and what would happen if they did. From asteroid impact to nuclear war, from exploding stars to the obliteration of all electronics by a solar flare, from rapid climate change to geoengineering gone wrong, and much more, we have a range from the total obliteration of the entire universe to “merely” massive death and destruction but the survival of civilization. Albeit somewhat singed and damaged.