12 year old cat bit kitten after he played too rough with his tail. The 12 year old seems to like to play by?

by lashing his tail to tease the kittens. When they get too aggressive, he stops them with a swat, hiss or in this case a bite. Should I discipline him? I think they are just establishing
territorial rights, it doesn't happen every day and we separate them when we're not home.
Answers:
Your cat has been in your life for 12 years, it is bound to have a few territorial issues. I would just watch them when they are around each other and separate them when you cannot supervise.
Maybe at twelve, your cat does not want to put up with the crap the kittens put him through! Ha ha Would you want an annoying child always pulling your hair or biting you?

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Don't discipline him. He's not harming the kitten, and he's just letting the kitten know the boundaries (trust me, kittens are stubborn and could use a swat/hiss/nip every once in a while).
I foster kittens on occasions, and my adult cat does the same. Starts with a hiss, if that doesn't work, then a smack. Bites usually happen when the kitten continues to persist.
The most I do is say ''Cut it out!" and move the kitten away from the adult cat.
Kittens might just be too rambunctious for your 12 yr old cat.