Why does its age come in to play? The think they are listening to is old too. The main thing is the size of the dish that allows for it, and then the skills of the operators to find the weak signal in the noise.
They were referring to Dwingeloo [1] in the Netherlands, the telescope used in this article, not Arecibo. It stopped officially operating as a radio telescope in 2000, and has since been used for a variety of astronomy and amateur radio projects.
Because the object you are receiving a signal from is further, thus necessitating more sensitive receiving equipment that couldn't have existed in the past?
Superconducting detectors and materials science have obviously advanced leaps and bounds in the last 30 years: it's really not up for debate or a premise that can be "bought."
