
Yep there ahve been many males who have never sired litters as by the tiem they were given the opportunity they couldn't get the hang of it or were infertile.
On the other hand a male I bred was used at 6 1/2, as he happened to fit in with the bitch, adn has sired four more litters, he is now 9 years old and I expect won't be used again, but has produced a nice sound son, which has been used, so may be of use to me in another generation, but too close for now as his Mum is half sister to my Lexi.