M.P.
My kids started staying with the grandmas at about 6 mos old. They live close by and it's so wonderful to get a break every now and then. My mom and MIL handle them like pros! Grandmas rule! :)
Just plan on wearing him out so that he goes down easy at night. He will be fine and you two will have so much fun! It's so important that kids get to bond with their grandmas!