Yes the minium is 5 to start a troop (at least at the Daisy level) but there are what the Scouts call Julliettes which are scouts in everyway except for the meetings... but I dont think that is at the daisy level...
And the new guidelines are ages 5/6 or in K...
Anyone interesting in information should go to the GSA website posted on the top of page two of this thread to learn more... there are also local chapters all over.