Is the fur coming out by itself or when your brush it? If it is not brushed at least once a day it will mat and then those mats will come out in the brush as clumps. With my two their baby hair grew out and became adult hair and just kept trimming the ends until the baby hair was gone. Laddy's hair broke coat on his head about the same age as yours with the gray roots. I had posts just like yours back then
. I thought there was something wrong with him lol. If it is coming out in clumps without being brushed or you see bald areas I would get him to the vet for skin scrapings.