So, to summarize:

1.) There is no other life form in the galaxy 2.) There is, but their probes are undetectable 3.) There is, but the probes hide before we reach maturity 3.) All life forms in the universe are of the same biological age as us (Moore's law)

Did I miss anything?

ad 1.) well, extremely unlikely with a lot of philosophical rammifications ad 2.) possible - we should find out soon ad 3.) unlikely - if there is more than one alien civilization doing this, one of them would not have had the desire to hide from us ad 4.) looks more and more like the real deal.