Old enough to have enough Objective-C protocols and categories in action.
The kind of documentation that inspired Java authors.
https://cs.gmu.edu/~sean/stuff/java-objc.html
https://en.wikipedia.org/wiki/Portable_Distributed_Objects
https://en.wikipedia.org/wiki/Distributed_Objects_Everywhere
Quite a lot has changed in objc since the nextstep days! And a lot more changed as Apple learned from that and built swift. My guess is you don’t know these languages as well as you think if you’re not clear about these differences.
(as a sibling comment pointed out, swift protocols are typically used for things that in objc you would use inheritance)