i'd say it solely depended on the weight/fat weight of a person, their lifestyle and their metabolism...

just guessing here... but as an example under my theory.. a 300 lb person that's like 6 foot that doesn't get much excersize and has a slow metabolism would take by far, much longer then a 6 foot 120 pound person with a very fast metabolism and an active lifestyle.

cuz the only thing that really explains tollerance, is the fact that by-products of the bud stay in your system, thus your body is used to having it there, and it takes a lil more to get the same effect as if you're clean... and since thc is stored in fat, that's why those factors would greatly affect tollerance.