Are different types of dogs bred at different ages, or is there a standard age at which breeders breed dogs?

My daughters and I were debating whether all types of dogs are bred at a certain age or whether it varies by breed.

Are bigger and smaller breeds bred at different ages?

Do you have any websites that are good to visit about different breeds of dogs.

Please no ranting, our dogs are fixed.
Update: Wow! I learned so much from everyone. Thank you to all! But I can't decide because each answer had a lot of merit. You guys gotta decide it for me, please. I respect each and every oppinion offered here.
12 answers 12