At what age can guppies become pregnant?

As far as I know female guppies reach maturity at about 3 months, and males slightly earlier.

Elmo that is about right also I think that they can get pregnant in a few weeks too.But keep in mind that if you want to breed bigger and better quality guppies you should seperate the males and females so the females can grow before breeding.You get better and more fry that way.Just my input.

Female guppies do reach sexual maturity earlier than males, but only by acouple of weeks. The sexual maturity of females is reached at just 3 to 5 weeks of age, but I would not recommend breeding them at this early age as, although they are fully developed, they should be allowed to grow a bit bigger so they can cope with the pregnancy better.

Hope this helps,
Michael.