According to multiple sources, kittens can have catnip, but they may not react to it until they are at least 3-6 months old. This is because the ability to appreciate the herb is genetic, and kittens under the age of 3 months dont react to catnip at all. However, some cats can be exceptions to this rule, as they will slowly increase their sensitivity over the years. It is safe to give catnip to cats of all ages, including kittens, as it is a very safe and harmless herb for cats. Nonetheless, pet parents should be mindful not to overdo it and limit the amount of catnip given to their kittens.