Things are even worse for intelligent life. Because we only could understand et with similar to our level of sci/tech development, but what if we encounter civ

Things are even worse for intelligent life. Because we only could understand et with similar to our level of sci/tech development, but what if we encounter civilization, even one magnitude older than our? For example, now our science have evidences about human civilizations up to somewhere 10k..50k years, and our current civilization oldest evidences are about 5k years. Imagine, how could look our civilization in 500k years? And if we use adequate considerations, human life was appear on Earth ~ 500 thousands years ago, and before was possible reptile civilization, for about 10 millions years, but our Earth become life planet ~ billion years, and exist planets in other star systems, which are tens billions years older than Earth. So what I mean, in our 5k years our civilization decided to re-circling resources and probably in ~ 100 years we could implement this decision and will become invisible to ets of our level. Imagine, what technologies would be available for magnitude older civilization. Could someone be sure about possibility of detection so much newer technologies? You may hear classification of seti scientists as Cygnus, Cancer and Pike. What I want to say, civilizations younger than our are detectable for us, but older are detectable only if them decided to contact us.