Males whenever they produce sperm plug, show interest and I feel comfortable with them breeding.
Females I personally prefer to breed large female however it varies on various factor.
While I would not breed a 18 months old female below 1500 grams, I will breed a 1200 grams females if she is 3 or 4 years.
Everyone does it a bit deferentially it's a learning process to see what works for you and your animals, it's also about being patient and remember because they are proper size or age does not mean they will breed either.