I think the OP was referring to experience not age. Older devs have seen the landscape change so much and if it makes full circle again that experience will pay off.
Experience can be valuable, but it's not automatically valuable. Plenty of people completely fail to learn from their long experience. Others learn very quickly from their limited experience.
The paragon is talent plus experience plus willingness to learn from experience. Admittedly, more older devs than younger devs will have this combination, but "social promotion" is no guarantee of success.
The fact is that there's nothing unique about any age group, and the only difference between them is their birth dates. Intragenerational differences are always larger than intergenerational differences. In any age group, there are varying degrees of competence, varying degrees of attitude, varying degrees of personal circumstances (e.g., home, family).
Ageism is treating a person solely as member of a group rather than as an individual. You simply can't accurately generalize based on a job candidate's age. Anyone who claims, "In my experience [members of age group] are mostly like this..." is putting forth weak anecdotal data that is practically useless and totally unscientific.