100k a day is.. routine, not even challenging for anyone who cycles regularly. They say cycling is a sport where you can peak around 50. The guys I cycle with are all well over 50 and some of them can seriously outpace me (I'm 31) I am sometimes overtaken at sportives by very old brown skinned skinny men on bikes. I'd say one of those guys would be able to do 200k a day np. (last sportive I did was 190k with 4 category 1 climbs in one day)