My dad had an undescended testicle until he was nealry 12 (so did his brother, and his daft parents waited until his YOUNGER brother was "old enough" for the operation, 10, and got them both done at the same time, even though my dad had hit puberty by then). When my dad was 14 he was fighting with said brother and his "good" (i.e. the one which had descended normally) testicle got twisted and the blood got cut off. He was taken to hospital but they couldn't save it - left it in situ but it withered away to nothing. He and mum had 4 pregnancies and 2 live-births from the undescended and too-lately operated on testicle and never had to try for more than a month, even though she was 38 before they started trying, so i wouldn't worry too much about fertility.

Bx