You might get some hints on this by looking at pictures of your grandfather in his later years. Sometimes baldness is a result of a medical condition, prescription drug, or chemotherapy for cancer treatment. Males tend to lose their hair in what's known as 'male pattern balding'. The resulting look is that of a horseshoe of hair around the back and sides of the head. Balding is generally a result of the hair follicles NOT growing any new hair shafts.
Hair grows for about three months averaging one.
The hair follicle then goes into hibernation for about a month. After this time period, a new hair shaft grows from this follicle and pushes the old shaft out. It's when the new growth doesn't re-start the growth process you begin to notice 'balding'. Also some follicles will gradually die, but most simply shrink to the size they were when you were born which produce weaker hairs. The hairs becoming thinner and thinner until they are too fine to survive daily wear and tear from washing and brushing it.