Having done in the same day 6 hours of psycho-technical and psycho-motor tests at Air France to get into their "Pilote Cadet" program (4h in the morning then 2h in the afternoon after a lunch break), I definitely felt my mental speed during high load+stress at 32 was already a lot slower than at 20 in engineering school. I never felt so brain exhausted and I concluded I was not that sharp anymore ...