> Intense bike positions require you to statically position the neck at almost 90 degrees to look forward
Cyclists learn that the proper position is to hold the head at roughly the same angle of the spine and to peer upwards at an angle. So you are basically looking UP, but since the top 2/3rds of the spine is tilted forward at 45 degrees, you end up looking forward. However, as the neck muscles tire from holding a 15 pound head this odd position, riders end up like you described.
> could easily just be age…
I'm pretty sure that's the case. :)