With 100bb stacks or less, it is extremely rare that it is correct to fold KK preflop. Like opp A raises, opp B reraises and opp C who is a nit shoves. Then you can start thinking about folding KK.
As Stargrinder said, not only it will only happen 4.4% of the time that your KK runs into AA, but even then you will still win about 1/5th of the time.
Refer Sammy Farha vs Barry Greenstein in season 1 of High Stakes Poker... The reason he hesitated so long is because of the depth of the stacks.