At about 2.5 to 3 years. Do NOT be surprised to find that your male suddenly goes off feed for weeks during this time during spring or summer.
Their first time of sexual arousal generally takes priority over feeding. I'm not sure whether for subsequent years the yearning is as strong.
Breeding partners should be as close to the same size as possible. Maybe even a larger female who has been recently fed. (I know of one breeder who used a 33" and 36" snake only to come back and find that he only had one larger snake left.)
Mex Blacks are totally unique - we are lucky to have them as animal companions!