I think the folk definition of aging is actually aligns quite closely with the probability of death definition.<p>Consider the phrase &quot;He looks like he aged 20 years, but it has only been 5 years since I last saw him.&quot; Everybody understands this to mean that he looks like his health has declined in 5 years the way most people&#x27;s health would decline in 20 years.<p>If you replace &quot;health has declined&quot; with &quot;probability of death has increased&quot;, then it means roughly the same thing. 
It is true that the folk understanding of &quot;health has declined&quot; could be based on several proxies such as skin texture, baldness, etc. I think what the probability of death definition does is bring some precision to what you mean when you say &quot;health has declined&quot;.