I think it will be no longer than 10 years at this point.
Unless the U.S. finds another way to give itself a shot in the arm and hobble along for another 25 years (which is possible, I guess) - this country is cooked. It is already so much different than even 2 years ago, just in terms of general consciousness, that if this trend continues, it will fall within our lifetime. Like others have said the contradictions are becoming ever stronger, other countries are increasingly powerful and most notably China and the global south are rapidly growing.
The U.S. will not be able to win a war without deploying nuclear weapons and obliterating the entire world along with itself. I wouldn't put it past them to try if/when it comes to that, but the period of domination where they could fend for themselves is gone. Recruitment rates are in the shitter and again, the general population is extremely unhappy with the way things are going. Class consciousness still has a way to go, but we're getting there. It's not like it takes a whole country to complete the initial stages of a revolution, and more and more people are getting radicalized by the minute.
Ultimately, it's going to take a serious world event that weakens and splits the bourgeois of this country (which is already kind of happening) and the swift action of the masses to take advantage of that when the time comes. It absolutely has to be soon, not only do I believe that it will be, but it has to be, or climate change and the US lashing out will genuinely cause hell.
In our lifetime ain't just a saying, people. Get out there
Currently working at a UPS warehouse - I am a physically fit young adult and the shit is still grueling. I feel you heavy.