In a wonderful example of what I have decided to spend my precious moments on, I've actually played Cookie Clicker through to 99.9% completion. That is: all the achievements (but one), and all of the upgrades. And then some game+ as well.
Your calculations are overlooking a very, very important part of the game: the upgrades to your purchases. They increase cookie production by percentages, or double the output (multiple times), and so on. Getting achievements also adds to your cookie production (a certain percentage). And then soft-resetting the game gives you an automatic bonus in the form of a reward for total cookies baked at time of reset, in addition to the same bonuses you were receiving from achievements from your last game.
So no, not objectively lifetimes. I played for about 5 days.
My coworkers, on the other hand, have been warring in the office over it for 15 workdays...