I think this blog post of mine from 2007 gives a better (or at least more succinct) answer to this question: https://thelocalyarn.com/article/this-is-your-life
Any explanation that doesn’t say anything about the mind is just baloney. Time here is an experiential phenomenon. It’s not fractions. Insert your pet theory in a context where adults have the same mindset as children and retain memories perfectly and have no reason to discard/compress memories them—you see that it’s totally irrelevant whether your life is 2/3 or 1/8 over. It has everything to do with how the mind works, not how numbers work.
Bonus points for the “unscientific representation of your potential cumulative effect”… which is very self-aware-useless.