Kittens can eat cat grass at 8 months old. Kittens aren't born knowing how to vomit hairballs; generally, they learn around eight months old. At this time, it's more appropriate to give them hairball remedy. Also, kittens have short fur and lick less, so there's no need to induce vomiting by feeding them cat grass. It's recommended that cat owners wait until their kittens are over 1 year old before introducing cat grass to prevent hairballs. For long-haired cats, you can start a little earlier, depending on the kitten's development. 
Cat grass feeding precautions:
1. Do not feed cat grass to very young kittens. Kittens are not born knowing how to spit out hairballs; generally, kittens learn to do so around eight months old. At this time, it's more appropriate to give them hairball remedy.
2. Do not feed cat grass to pregnant cats. Pregnant cats require careful care, and feeding them cat grass can cause vomiting, which may lead to miscarriage.
3. Do not force-feed your cat. If your cat doesn't like cat grass, it may be because it feels uncomfortable after eating it and has difficulty eating. Cat owners should adjust their feeding methods accordingly, such as mixing the cat grass into the cat's kibble or canned food.
