In short-lived mammals, age at maturity is a particularly important parameter influencing lifetime fitness. Age at maturity proves highly variable in altricial rodents, but little is known for small precocial rodents of the order Caviomorpha. Even though extreme precociality implies early maturation, female cavies and guinea-pigs (genus Cavia) advance puberty considerably in the presence of males. We briefly review earlier findings and compare them to data from altricial rodents. We report experiments on 2 very similar species of cavy, the dark-backed (C. magna) and the wild cavy (C. aperea). In the dark-backed cavy, we tested whether the male signal responsible for acceleration of maturity is a chemical in urine, as demonstrated for mice. Females exposed twice daily to male urine on their nares matured at the same age (73–75 d) and mass (around 330 g, 4 times birth mass) as females treated with water. Thus, chemicals in urine did not replace the effect of male presence. Two experiments with wild cavies showed that male presence without physical contact was sufficient to accelerate puberty, even though physical interaction leads to even earlier maturation. Presence of a male during the first 10 d of life only did not lead to advanced maturation in young females. Functionally, it may be more correct to speak of a delay in the onset of maturity in the absence of males rather than considering male presence to stimulate early maturation. Comparative evidence suggests that precocial species generally mature earlier than altricials.