Thank you !!!Day one.
Use positive reinforcement, there's nothing to be gained through punishment and it will only damage your relationship. The bond is everything for a zoo, do everything you can to make it strong and based on love and respect.
If you mean train *for sex*, you don't, not at any age. When they grow up, if you've taught them that you are kind and loving, they will usually come to you with their desires.
Very well explainedSex is a natural instinct; they don't need to be trained to know how to do it cause they're born knowing how.
When he starts showing interest in sex, all you need to do is show him that you'd like it if he did it with you by using body language and touch. If he's interested, he'll have sex with you, if he isn't... you'll probably know right away. Like what egoldstein posted, just focus on being a good human and a good companion to him.