When I worked on Fiber wifi and sat on the second floor (after it was renovated with a "movement" theme, but still kind of dungeony), David sat across the aisle from me. I didn't know who he was at first, and just thought of him as "perhaps the only extant person my parents' age who listened to the same music I did in middle school".
(And when Fiber's headcount got substantially cut and I needed to find a new team, I ended up working in "Kornistan", so named because the org was run by David's son Jeff.)
68 year old engineers have usually retired long ago by choice. Engineering pays well. There aren't many 65-70+ year old engineers who are even still interested in working, let alone keeping up with modern technologies.
Anyone sticking around that long at a famous company is almost certainly in it for the love of all things computers, not because they need the money.
(And when Fiber's headcount got substantially cut and I needed to find a new team, I ended up working in "Kornistan", so named because the org was run by David's son Jeff.)