No dog should be bred before their health testing is completed (usually at around 2 years). There is an age limit for females, because their body & reproductive system has to be mature enough to safely carry & raise a litter of puppies.
Allowing them to reproduce too young is VERY dangerous for the dam, & can be life threatening. Their little bodies just aren't ready to endure the strain of pregnancy, delivery, & nursing.
Males don't have to endure all this strain, they are considered sexually mature much earlier than females mostly for this reason. Keeping an intact male without allowing him to breed is dangerous (risk of infection, aggression, etc) it's like having an itch they just can't scratch.
It's smartest & safest to have both males & females altered, it reduces the risk of illness, infection, & behavior problems.. which it turn makes for healthier, happier pets.
Shannon Mommy To:
Johnny-Bravo Fawn/White June 1999 &
Donte Flashy Brindle Boy, June 2005 both docked & natural.