I think Tsavo lion may have a point about including older stars in the probable candidate for intelligent life. Since either a civilization is violent and short lived or peaceful and long lived. If short lived then we will probably not detect them. Since chance of coincidence of coexistence is low in small time quanta. But if long lived, then good chance. And this civilization will probably not depend on energy from their old star.
Have question for you. In nearby stars to earth. Say 100 light year radius. How many stars have the closest age and size to Earth? Has SETI looked here?
It looks as though, Earth like planets are common. And we know that on our Earth, life occupies every corner. And that humanoid bipedal life is the preferred form to develop intelligence. There existing several human species that could have become technological. Therefore it is safe to say, intelligent humanoid life is common in nearby stars. So the only reason for there being no contact, to my mind, is the short life span of these societies together with these evolutionary periods not being coincident in time. That is why I asked, did nearby stars form at the same time as our sun ?
I think that some here say with certainty that we have been visited. I say, that given the evidence, that some instances are probably of genuine visitations. By much more advanced beings, who remain hidden and are studying the planet. It makes sense why a more advanced civilization, may want to remain hidden. Since we have nothing of value to them for exchange. Nothing but trouble. And less advanced life is not exciting to us. We tend to kill them or eat them, here on Earth. So only an equal or near equal civilization can be practically of value to us.
I also think that most alien civilizations are short lived. Given the example here on Earth. May be a life span of 1000 years. So we must target our search to stars that have a very close age to our own star. Is it possible to predict accurately the age of star? To within a million years or even less? I think that is what we need.