My parents had an older cat (10-15 yrs at the time) and within weeks of getting some younger cats the old cat was treating them like her kittens.

Cats can be finicky, sometimes they warm up to each other and sometimes they don't.

Old boy might feel extra protective of his treats. You may want to take them out of the equation during interactions. Otherwise, just take it slow and steady, keep up the supervision for a while, and let them do their thing if no one is getting hurt.

I introduced two kittens to a 9yo cat several years ago. Our old lady is also a very sweet cat. To the kittens, she kind of acted (and still acts to some extent) like an auntie who isn’t afraid to tell them what’s what with a hiss or a bap, but it’s never very mean. Nowadays one of them will give it back to her, too. They don’t cuddle, but they all get along fine now and both “kittens” (they are almost 6 now) clearly like the old lady and will often sit near her. I think you have to give your old man a chance to make sure kitten knows that he’s in charge, and the way they do that is by asserting their dominance with a his or a bap. No claws is a great sign.

For what it’s worth, we also had to let our cats make sure the dog also knows who is in charge, lol. And she definitely knows!

What kind of cat is an ass man?