But what if that older dev is only at par with the younger one: will she or he be treated equally, if everything else was equal? In other words, is an old person expected to compensate for her or his lack of youth by an excess of wisdom?
They shouldn't be expected to compensate for their lack of youth in any way, as youth isn't a metric that has any relevance to their work in software development. And if they are of the same title/total comp as the young dev, there is nothing wrong with them being on par in terms of skills/knowledge/responsibilities.
Interesting thought though, what if the product in question is a product geared toward a younger audience that younger devs are more "in tune" with? Assuming they have more impact as a result.