The data in this piece: “Boards Talk About Diversity. Age Is the Exception” from PeopleReturn (formerly DiversIQ) depicts a slow but steady increase in average director ages over the past decade across the S&P 100, S&P 500, Russell 1000, and S&P 1500 indices:

By age group, the data reflect a much more noticeable shift toward older directors across indices, with the over-65 group representing 42% - 43% of all directors today vs. 36% - 38% in 2016. Comparatively, the percentage of directors under 50 has declined from 6% - 7% in 2016 to 4% - 6% today.

Average director tenure is stable at seven-to-eight years, albeit with a reduced percentage of directors averaging 15 or more years of tenure and a higher percentage of five-to-10-year-tenured directors.
The article merely suggests that age/generation, along with other forms of diversity, be among the board/strategy alignment considerations.