How Old Are Guinea Pigs at Pet Stores?

Guinea pigs in pet stores are typically 8-12 weeks of age. However, there are a lot of factors that affect the age of these guinea pigs, so it’s hard to know exactly how old they are. If the guinea pig fits in the palm of your hand, it’s likely 2-3 months old.


Getting a new pet from the pet store is an exciting event. Guinea pigs are particularly fun, as you never know what kind of personality your new friend will have.

But before you make the big purchase, you may wonder exactly how old the guinea pigs in pet stores are.

The simple answer is that they are between 8 and 12 weeks of age. However, that is a very loose assumption. There are a lot of factors that affect the actual age of the guinea pigs in stores.

While it might be difficult to know exactly how old they are, some general rules can help narrow it down.

Separating a Guinea Pig From Their Mother

The age a baby guinea pig can be separated from its mother plays an important part in understanding how old guinea pigs are in stores. Stores shouldn’t sell guinea pigs that are too young to be separated from their mothers.

Nursing and weaning

When baby guinea pigs are born, they rely on their mothers to care for them. This includes nursing. Most guinea pigs will nurse until at least 2 weeks of age.

However, if possible, nursing should continue until three weeks of age. Baby guinea pigs shouldn’t be separated from their mothers until they are fully weaned.

Males Vs. Females

Another important factor determining when a baby guinea pig is weaned has to do with the guinea pig’s sex.

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This may seem silly to consider when thinking about weaning, but male guinea pigs can reach sexual maturity by the age of 3 weeks. Because they reach sexual maturity at such a young age, they risk impregnating their mother.

This may not seem like something that would happen, but sexually mature males don’t think of their mothers the way we do. They see a female and will mate with her if given a chance. For this reason, male guinea pigs should be separated from their mothers by 3 weeks of age.

Females don’t run the risk of impregnating their mothers. Therefore, it is okay to leave baby female guinea pigs with their mothers longer. Ideally, female babies will stay with their mothers for four weeks before being separated. This gives you an idea of when a guinea pig can be separated from its mother, which affects when it can be placed for sale in a pet store.

The Various Age Factors

Understanding when guinea pig babies can be separated from their mothers helps determine the age of guinea pigs in pet stores, but it isn’t the only factor.

While they are typically eight to twelve weeks of age, that isn’t a rule. It’s possible that they were kept with their mothers longer. It is also possible that they weren’t immediately placed in a pet store after weaning.

There is also the question of how long they have been in the pet store. Even if guinea pigs were acquired by a pet store at 8 weeks, they might have been in the store for several months. It’s also possible that the guinea pig just came into the store the day before.

There is also the possibility that someone took the pet home, kept it for a short time, then returned it.

All of these factors can affect the actual age of the guinea pigs in pet stores.

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A Quick Trick to Indicate Age

Here’s a quick age assessment trick. When you are in the pet store, ask if you can hold the guinea pig. If the guinea pig fits in the palm of your hand, this is an indicator that they are quite young. Adult guinea pigs are just under 12 inches long. This isn’t necessarily the most accurate age indicator, but it gives you a place to start.

While holding the guinea pig can give you a quick and rough idea of age, further examination may help you make a more accurate guess. If you examine their nails, teeth, and body, you may be able to get a better idea.


Looking at a guinea pig’s nails can help you determine if the guinea pig is young or an adult. The nails of a young guinea pig are very short, pointy, and translucent.

As guinea pigs age, their nails become thicker and less translucent (they become a cloudy white color).


Baby guinea pigs are born with small developed teeth. These teeth are white and will grow shortly after birth. Their teeth will stay sharp, thin, and white throughout their first year of life. As guinea pigs age, their teeth will become dull. When they are seniors, they may even chip or break.


Baby guinea pigs reach about 18 ounces by the time they are 3 months old. Guinea pigs usually weigh around 24-42 ounces by one year of age.

It can often be difficult to determine exactly how old a guinea pig in a pet store is because so many factors determine the age. Typically, the guinea pigs in pet stores are between 8 and 12 weeks of age, but a quick examination will give you a better indication of their age.

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