When do balding men finally stop losing their hair?

Never. Balding or male pattern baldness is a progressive physiologic change that occurs to varying degrees as men age. It's an inherited trait that effects people differently. If you suffer from hair loss, topical and oral medications exist to help maintain the hair you have and transplantation procedures exist to reposition and mask the bothersome hair loss areas.
Varies. It is a genetic predtermined pattern and called pattern hair loss. The earlier you lose hair the more pronounced the amount of hair loss will probably be. If early minoxidl and or Propecia (finasteride) can stabilize the hair loss.