There's lots of room to nitpick the evidence, but the studies are published:
> The relationship between age and job performance for Air Traffic Control Specialists (ATCSs) is an issue that has been revisited many times over the past few decades (Trites, 1961; Trites & Cobb, 1962; Cobb, 1968; VanDeventer & Baxter, 1984). Researchers have consistently found a negative relationship between controller age and performance across studies that have used different ATCS options (enroute, terminal), career stages (age at entry into training,current age on the job), and criterion measures (on-the-job ratings, academy performance) (Trites, 1961;Trites & Cobb, 1962; Cobb, 1968; VanDeventer & Baxter, 1984).
> The relationship between age and job performance for Air Traffic Control Specialists (ATCSs) is an issue that has been revisited many times over the past few decades (Trites, 1961; Trites & Cobb, 1962; Cobb, 1968; VanDeventer & Baxter, 1984). Researchers have consistently found a negative relationship between controller age and performance across studies that have used different ATCS options (enroute, terminal), career stages (age at entry into training,current age on the job), and criterion measures (on-the-job ratings, academy performance) (Trites, 1961;Trites & Cobb, 1962; Cobb, 1968; VanDeventer & Baxter, 1984).
Via https://www.tc.faa.gov/its/worldpac/techrpt/AM99-18.pdf