No three months is not too late. Just get some blocks and a fairly treat hungry puppy. Put the blocks up on a table and then put the puppy up there. Treat them for being on the table. Then I try to pick up the puppies front and place both feet on a block. Hold a treat in front of the puppy so he doesn't move his feet. Then put your hand between the rear legs and lift him onto the other two block. This takes practice for person nad puppy. Then once they are standing how you want treat, and keep treating. It may take a number of sessions before your pup is standing still. also, even if he is you may want to pick up one foot at a time and set it back down to practice stacking, and to get the pup used to having each foot handled seperately. Good luck!
and the cattle dogs