Nick Bostrom says it's one of the worst discoveries we could make. Especially if the life is complex like animal life. That would greatly increase the probability that the great filter is ahead of us instead of behind us.
That, or the window of technological development that we can detect and are capable of recognizing as intelligent is very small. It's possible that superintelligence is all over the place, but we're unable to perceive or comprehend it, in the same way that a nematode is completely oblivious to human society. Once a society creates superintelligence, they might even "clean up" after themselves, so that traces of previous stages of their civilization aren't available for us to observe.
I don't think that's likely. Earth is billions of years old but we have just been around for a few thousand. If we an alien world had evolved just a few thousand years earlier, it could have colonized the galaxy by now. We can't possibly be synced that perfectly. All sorts of random events, like asteroid collisions, had a huge impact on the timing of our evolution.
>we're unable to perceive or comprehend it
That doesn't seem likely either. An advanced civilization could easily build many kinds of megastructures that would be detectable to us, like dyson spheres. I also think it's very unlikely they wouldn't interact with us. Either to help us if they were moral, or to exterminate us if they were not.
The fact the circumstances for intelligent beings took so long may have been random circumstance. There's no guarantee it would take that long on other planets to go from general life -> intelligent beings. The environments could easily be more welcoming to it, they may have had fewer extinction events restarting growth, etc, etc.
If it's as easy to make a nuclear-class weapon as it is to make a microwave, for example. That would probably be the end of us.
We're already kind of doing this with drugs and digital simulations...