My son only has one testicle that has dropped down right now. The doctor says the other one hasn't drop yet and they might have to do surgery. He just turned two. I was told that sometimes one of the balls doesn't drop until after they turn 2 years old.
An undescended testicle is rare, but more frequent in premature boys. The recommendation is for surgery to be done between six months and one year of age. Lack of treatment can lead to a higher probability of testicular cancer when he is a teenager or young adult, or infertility when he is an adult. The sooner your son has the surgery, the less likely he will have complications from his undescended testicle. I assume the surgery has been put off this long because you have been objecting.
The testicles require a cooler environment than what is present inside the body. If the testicle has died, the surgeon will remove the dead tissue so that it does cause future problems. Even with one testicle your son can grow up healthy and be able to have children.