People overestimate the mental decline that comes with age dramatically. It&#x27;s more sporadic: most people decline very little, while a few people (i.e. those with dementia) get hit very hard. Unfortunately, much of society forms its model of &quot;old people&quot; based on the &quot;hit very hard&quot; category, and not people like Jacques Barzun, who did his best work in his 80s and 90s.<p>There&#x27;s something you observe with biological mental illness which is that it&#x27;s more stigmatized than it deserves because people encounter the &quot;raving, crazy&quot; people with it (the worst-off 2%) and not the other 98% for whom depression, anxiety, bipolar disorder, et al, are more accurately modeled as boring and often manageable health problems than as residence in an alternative universe. I think that the cognitive negatives of aging (typically mild to nonexistent, except in senescent brain diseases like Alzheimer&#x27;s) get the same smear.<p>In fact, various studies have put the intellectual peak age (in healthy people) anywhere from 17 to 65 (except for in language acquisition, at which we peak in childhood). That&#x27;s largely because the curve is so flat and individualized (e.g. some people peak early, some late) that it&#x27;s impossible to tell.