Male cat 11 years old neutered will grab my sleave or a blanket, purring and kneeds with all 4 paws. He seems to get off on it
What do you think he is doing?

He isn't 'getting off on it'. My cat does that all the time, kneeding and purring, she is just getting comfortable and settling down. Give him a break, he has probably forgotten all about that aspect of his life, he is geriatric now, so enjoy his indosyncrasies at that good old age.

Tick

It's a comfort response. It means he feels safe, warm, and happy. It's a good thing. He loves you and feels comfortable with you. It's not sexual at all, it's part of the kitten suckling action.

If his claws are pricking you, then put a thick blanket, or folded corner of a blanket, between you and his claws.