Here are some TT times from the Revenge of the Disc TT, 2018
https://obra.org/events/25868/results

Unfortunately I can no longer find the race details, and the junior races were shorter than the other races. Winning Times:
Cat 1/2...... 1:23:57
Cat 3..........1:25:30
Cat 4/5.......1:25:25
Mast 40-44..1:27:35
Mast 45-49..1:24:01
Mast 50-54..1:26:51
Mast 55-59..1:26:32
Mast 60-64..1:28:32
Mast 65-69..1:30:46

And then to a shorter course for the 70+


I think they changed the course. My notes for 2017 indicate 24.8 miles.
https://obra.org/events/25095/results
Cat 1/2...... 54:53
Cat 3..........55:52
Cat 4/5.......1:00:32
Mast 40-44..59:55
Mast 45-49..55:49
Mast 50-54..57:12
Mast 55-59..58:31
Mast 60-64..1:01:04

Anyway, the old geezers are going mighty fast, averaging about 25 MPH. Maybe a slight degradation over time, but many of them could hold their own with at least the Cat 4/5 group.

And, I was thinking I could take up racing in my 50's, and it would be like a walk on the beach.