The interesting thing about brevets is that everyone who completes the ride is a winner.
It doesn't matter (on a 1200km ride which has a time-limit of 90 hr) whether you finish in 50 hours or the full 90 hours.
Ken Bonner, for instance, who is 64 or 65 (I think), has completed many 1200 km rides. His most recent was from Boston to Montreal and back to Boston (BMB) and he did it in 59 hr, 49 min.

Others in their 70's have completed the PBP 1200 km

The advantage of being older is that the quick twitch muscles (so essential for fast sprints) is no longer active; but the endurance factor is increased.