There is not that much caffeine in Red Bull surprisingly. It’s a lot compared to a soda but it pales if you compare it to coffee: it’s approximately half as much as what’s in an espresso. Caffeine-wise, drinking two cans should be fine (provided you don’t drink a ton of other caffeinated beverages).

Honestly my first guess here is that we are in the presence of a confounding variable. I can somewhat imagine the life style which goes with having to drink two cans of Red Bull everyday. The cause of the sleep problems starting at the beginning of early middle age might actually be found here.