I did an "Etape" ride last year .. 220 km's, 3000m (or was it 4k?) of climbing including one 1st cat climb. Pretty heavy for me, but I got through - something like 40% of riders didn't make the 11 hour cutoff.
At the start, they had a big panel with a list of all the riders. Out of curiosity, I did a quick scan of a bit of it and found someone who was 75. Noted his name, then checked the results after .. he beat me by 15 minutes.