I reckon minimum age is 2.5 years of age, that is if you feed them religiously weekly. In May/June normal daytime heat, nighttime no heat, aiming for nightime minumums of anywhere from 16-18 degrees. After 6 or so weeks of cooling , you will notice your males pacing up and down their cages, whack the male in with the female, on 3 days rest 2 days. Once you get ovulation back to 24hrs heat... done! Worked for me.