way too many variables for any sort of an extremely accurate answer and it ought to vary depending on time of day as well.
There are 6 ways (4 Choose 2) you can be dealt a pair of aces with 2 cards and 52 cards in the deck so there are (52 C 2) = 1326 possible starting hands.
So 6/1326 ~= .004525 or 0.453% chance of getting pocket aces on any given hand which works out to one time in every 221 hands or 1:220 odds
How man worldwide? Good luck estimating how many average hands an hour are dealt worldwide but it would be (your estimate here) * .004525 to figure out the avg. I'm not even going to guess.