Hi , laura is here first time to log in... from Chicago Ill ,Ermosa area and just wondering when does a male dog stop spearmaciding to reproductive system is there an age limit that a male dog can stop mating

Sperm production starts to decline after the age of 5, by 10 it is so low that most can not cause a pregnancy

We don't really know

Boys produce sperm throughout their lives...

Neuter him and it'll be guaranteed that he won't produce sperm.

My friend just had a litter of pups sired by a 10 year old and one of my mothers dogs sire was 15 when he produced her pup.

It varies greatly depending on the dog. You can get sperm counts done at vets.