The average human lifespan is around 75 to 85 Years old and if you live beyond 85 years old then you're basically lucky and on your bonus years.
As you get to your 60's the time seems to speed up so that one year may seem like only a month and so on and so forth.
There's really no set age that humans are supposed to live to naturally but if a human is living and gets to a point of having dementia in their old age then that is not considered natural.
I hope I live a long life and hope to make it to at least 100 years old but as long as I have a good mind and can take care of myself.
If I don't have a good mind or can't take care of myself then it's time for me to die and not be a burden on anyone.
Living with dementia is no way to live and the patient is not really living.