"What are the conditions to create culture (which is necessary for a radio telescope)? Some necessary conditions might be:

predisposition for social interaction and cooperation
ability to make complex tools (hands)
ability to reason symbolically (and communicate that way)
few offspring
minimum lifespan of say 35 years
competitive generalists (adaptive to complex environments)
successful enough before culture to build up relatively high density."

Two important things I think you omitted.

(1) The ability to pass on information from generation to generation about what has been learned via communication.

If one Octopi finds a piece of iron on the ocean floor and learns that it can use it as a tool to open clam shells that information is lost on the next generation it gets left on the ocean floor beside that octopi's decaying body when it dies.

If the information is passed on another octopi learns that the pointy piece of iron makes a good tool to ward off predators still another learns that it can be used to kill other octopi and keep them out of it's hunting area and other octopi learn to socialize and form gangs then armies and eventually take over the world.

(2) Socialization: Groups of octopi can share information they have learned, send their offspring to school, build large structures including octopi city the first fortified city.

Human's are not herd pack type animals by instinct IMHO.
We group out of necessity.