skinny gecko

Question
I have an African fat-tailed gecko that is 11 years old.  I feed him crickets about every other week, his diet has always been crickets. He does not like millworms. Eating is not the problem, but in the last 2 months he has gotten extremely skinny.  He still responds well to me and the children but he just seems to be shrinking in size.  I don't know what to do for him to help him regain his weight, his tail is no bigger than my pinky finger.  Please help we my concern if you can.  

Answer
 Like people, when reptiles reach the other side of middle age.  Their needs change and usually you learn these needs after a good geriatric check-up at his vet's.  Bloodwork will give you an idea if there are any medical issues, or change in dietary needs, or even if an increase in hydration is needed.