I had asked my mentor(been breeding 15 years) about my male that is over 2 years old and this is what she told me
"Males can breed for years until they can't get into the right position due to age issues. I have bred males at 5 years old with no problems at all. Your females will retire before your males.'
Some males can breed at 5 no problem but I've found that many become hit and miss once they reach late 3 or 4 years old. I think their fertility decreases as they age so even though they still can physically breed, they don't consistently produce babies.
My girls are retired by 3 and sometimes 2 depending on the individual girl. Some decide on their own when they are done. Figure on 4-5 litters for the girl, spaced every 6 months. Roughly at 6 months, 1 year, 18 months, 2 years, possibly 2.5 years.
I also retire my females between 2 and 3, and I have one male that is just under 3 years who that I used for breeding recently and the female didn't become pregnant so I am assuming his fertility has dropped and he will now be retired.