100’s easy with little/no training, i’ve done them within a few rides of getting back on a bike after an op, not pretty and not easy at the time, but keep eating and drinking and your heart rate below your threshold (this is the important bit, however fit you are if you go above this you will blow up, stick below it and you’ll be fine).
if you want to do it fast then join a roadie club, they’ll do 60 miles ish on a sunday morning in the slower groups, faster groups go further so you can move up as you get fit. If you don’t want to do it with a club then at least get used to riding without stopping/faffing about as thats the important thing on big days, you can go as fast as you like, but its the hours spent moving that actually get you to the end.
