That was my first thought as well, but I find it to be statistically implausible. It could be that humanity is on the cutting edge of advanced life in this galaxy, but highly unlikely. Even if life-sustaining planets have only been around in this galaxy for the ~4.5 billion years that Earth has existed, then surely intelligent life will have evolved on other planets at slightly different rates. Some planets would be faster, some would be slower, but the order of magnitude by which we interpret "faster" and "slower" would be in the hundreds of millions of years. So, for your argument to apply, then you must believe not only that life-sustaining planets can only have existed for the past 4.5 billion years, but also that on every one of those planets among the 100+ billion stars of this galaxy, it takes at least 4.5 billion years for microorganisms to evolve into highly intelligent life. Earth, and humanity, would have to be literally the galaxy's best habitat for the evolution of intelligent life, which seems like a bit of a stretch.
I'm not aware of any academic consensus about "post-physical" species, can you elaborate?
Nuclear war might not wipe all humanity off the planet (I disagree on the "very unlikely"). There isn't a consensus on that. And even if it didn't wipe out every single human, it might reduce humanity to pockets of survivors below the minimum sustainable population threshhold, which would eventually die off. In any case, I was only using nuclear war as an example of self-inflicted extinction. By the time we have interstellar travel, we will probably come up with even more effective methods of mass destruction.