You lose 10% of your ability to react and think quickly, not your ability to think. In fact, the older you get the more deep your thinking becomes. This is probably what you see when you think “John is slow to respond at times” (John being the older, 40+ developer). The reality is John remembers the last time someone suggested using MongoDB as a caching store and how well that worked out. John is recalling all those crunchtime meetings in the war room because someone wrote bad code or the software architecturally failed. The slowness to respond is them weighing all the options, for which they have more in the catalog than you. A binary search on 100,000 objects is fast (22 year old), a binary search on 1,000,000,000 is slow (a 40+ year old). Ageism is just fancy employment discrimination.