As Reggie is so young I think you should only give him a very small amount of peanut butter, perhaps just enough to smear thinly on the inside of the kong. It's very fatty and most varieties contain salt too, so it's really something to be given as a special treat and not on a daily basis.
Most dogs love it. My 2 adult Cockers think it's great and when I have peanut butter on toast they hang around and usually end up with a corner of toast and peanut butter