Good post but conclusion is wrong. "Life" exists elsewhere than Earth. The sole question is did their sentiency last long enough to get off the planet.
Earth is 4.5B; Big U is 13B; M-class stars with suitable planetary systems would have started forming 5-6B later.
That gives a 3B head start to other ur-Earths, which is enough time, enough chances, for a carbon-based, water-dependant humanoidish society to either get off their planet and get going, OR singularize with silicon-based forms and get off their planet and get going.
Then the question is, how many, where did each start from, and did any acheive interstellar flight.
3B is a looong time. YUGE. You could have hundreds of thousands of cycles where sentient carbon-based forms arose and failed to acheive interstellar flight. We may very well do the same thing.
Given that your sentence is in the present tense and given the space-time distance to other stars and galaxies, evidence supporting such a claim would seem to be limited to actual visits to Earth by extraterrestrial beings.