The inguinal canal, that is the canal through which the testicles descends after birth, closes for good between 12-14 weeks. There are very few (rare) exceptions to that. After 12-14 weeks of age, testicles are where they will be.
Undescended testicles are 13.6 times more likely to become cancerous. Likewise, there is a much higher risk of testicular torsion, where the testicle twists and cuts off the blood supply. This is about as excruciatingly painful as it gets for a dog.
You should really begin considering having your dog neutered.