How do you know when a male chihuahua is ready to breed??
If your dog is AKC registered you will need to check the guidelines on your breed to see when they will accept a litter from him. A Chilhuahua is a pretty sexually active little guy so I would think 8 months and up. The reason I am using 8 months is that is the age my Boxer and Boston males have to be to be used for Stud.
Now have you tested the female. Do you know if she is free from diease? Does the male or female have any genetic defects that you don't want to pass down to the pup. Only breed if you have a very good male.
If you are not wanting to breed and want to neuter him 6 months is the age to consult with you Vet. about getting your male neutered. He will begin to hike his leg and start the male habits at this age.
When he starts trying. He will sniff her and will try marking his teritory Its normally around 9 months when males are ready.
if you have a male and female then it could happened any time after they get older
Hope this helps: http://en.wikipedia.org/wiki/Chihuahua_%28dog%29