As soon as the testicles have desended I believe, which happens around 6 months, or earlier, I think. However, unless a female is in heat she cannot get pregnant. Females generally have their first heat between 6 & 12 months of age though. So a 5 & 7 month old pair is very risky. That is plenty old enough to get spayed & neutered even for the most conservative vet or owner.
A sirloin roast of 8- to 12-lbs will take 16-20 minutes for rare, 20-22 for medium rare, 23-25 for medium, and 26-30 for well done. A boneless top round, by contrast, will take 28-30 minutes for rare, 30-33 for medium rare, 34-38 for medium, and 40-45 for well done.If you roast at 325Â°F (160Â°C), subtract 2 minutes or so per pound. If the roast is refrigerated just before going into the oven, add 2 or 3 minutes per pound.ow long and at what temperature should I cook a beef roast in the oven? Roasting is a great cooking method for a large, tender cut of beef  such as a rib or sirloin roast.
Top rounds will also make outstanding oven roasts. If you purchase an eight inch London broil and then cut it in half you will have two very nice 4-5 pound roasts. Top rounds can be cut into very nice stir fry, stew meat or Swiss steaks or just ask the butcher to grind some of them for nice and lean ground round.