The most common problem associated with undescended testis
is reduction of fertility
It has been found that fertility problems are more in cases where both testes are undescended and if treatment is delayed.
That is the reason why surgery is recommended as early as 6 months of age, atleast within 2 years.
Also there is a slight increase in the incidence of germ cell
tumours of testis when they grow up.
But the possibility of fertility reduction should be borne in mind and you may have to discuss that with your Pediatric surgeon.
Hope my answer helps you.
Wish you good luck.