Earlier than the sixties? All elements of OOP were known before 1967, but their combination, which we still use today under the title OOP, appeared in Simula 67 for the first time. I think the first appearance of a GC in literature was in 1960.
I think, the first mark‑and‑sweep collector was published in McCarthy's 1960 Communications of the ACM paper "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I". It's resonable to assume, that they already had it when Steve Russell implemented the first Lisp evaluator, but we don't know exactly when it was added.
No, that paper doesn't describe the garbage collector. I do think it is true that before it was published Slug Russell had implemented the GC, but I think it's correct that we don't have listings from that early.
Edit: yes, yes it does describe the garbage collector.
Yes, but ideas are (mostly) worthless. I mean, they are necessary, but that's the easy part, building the technical foundation that make it possible is the hard part.
The internet needs wires and routers, distributed computing need a good network (i.e. the internet), current-day AI needs GPUs and GPUs need silicon chips that defy the laws of physics. Really, looking at the EUV lithography process makes all of computer science feel insignifiant by comparison, everything about it is absurd.
The real progress is that now, we can implement the ideas from the 70s, the good ones at least. I don't want to diminish the work of the founders of computer science, there is real genius here, but out of the billions of people on this planet, individual geniuses are not in short supply, but the real progress come from the millions of people that worked on the industrial complex, supply chains and trade that lead to modern GPUs, among everything that define modern computing.
"Fully specified" is the important part here, and the work that went into making the idea fully specified is where the value lies.
For this, we could look at intellectual property laws. Ideas are not protected. Neither by patents, nor copyright, nor trademark. If you want to make your idea worthy with regard to the law, you have to "fully specify" it, turning it into an invention (patent), or code (copyright).
Rather from the sixties. E.g. OOP including dynamic dispatch, late binding, GC etc. appeared 1967 with Simula.