I have a working thesis regarding age. Age can be thought of as broken up into three phases: young, middle aged, and old. Life expectancy is actually a little less than 80 now, and has dropped a couple years because of the pandemic. But, let's say that average lifespan is about 75 years. A couple years greater or less doesn't make a difference for my point. 75 is a good number to work with since it divides by 3 easily. So, taking 75 as the average lifespan, then the period of birth to 25 should be considered as the "young phase" of life. The period from 26 to 50 would be the middle phase. And the period from 51 until 75 is the old phase of life.
I know that no one wants to hear this, but that's pretty much how it works out. If you're 54 and need to tell yourself that you're at the "younger part of the old scale", then by all means go ahead and do that if that is what you need to do.