Can you grow a full head of hair on a bald man who is 65?

No. That is not realistic, but current science can revitalize any hair follicles available to wake up and start growing again, or if a hair follicle is producing a hair, we can get it to grow a stronger, thicker, longer hair. The longer the amount of time a hair follicle has not produced a hair determines the success in returning that follicle to a state of growth, it is best if the follicle is still producing a hair in the first place, and even better still if it is producing more than a miniaturized or very fine thin hair.