> But if you to try to objectively answer a more abstract question, "Is it better for humans to live to 150 years of age rather than 75 years of age?", I don't think there is objectively a right answer.

This answer depends on the definition of what is "better".

Is it "better" to have two "medium" happy people or one "very" happy person? On a societal level, should we be measured by collective happiness (the sum), average happiness, the most happy person, or the least happy person? Or maybe "happiness" should not be the measure at all. Evolution dictates that the "best" is the one that survives the longest as a species, so maybe we should tune society simply for long term survival, regardless of happiness. Or maybe you believe in god, and "be fruitful and multiply" is the standard, so the more the better, regardless of other criteria. Maybe the answer is to maximize GDP. Or perhaps seeking knowledge is the pinnacle, so any society that builds the largest pool of knowledge is the best.

There are countless other ways of determining "better". Take a philosophy course and dig into it.