Reason for the coffee probably far worse!
I'm guessing that the lack of sleep, most likely being the cause of over-consumption of coffee probably does far more damage than the coffee ever will.
Plus, if you're drinking that much coffee, and not consuming (body weight in lbs / 2 = oz) enough good water + whatever oz you drank in coffee (to compesenate for the diuretic effect), you're doing a lot of damage there too.
And, then if you've got the typical S.A.D. (diet) going, Alzheimer's is probably the least of your worries! Obesity, cancer, diabetes, etc. are going to get you way earier.