OK, what have you started?
Here I am. Regularly doing 30 miles in a day. 2 x 15 milers.
Occasionally going out with a 'novice' tri club doing 30-40 miles in the Peaks and my longest ride to date is probably around the 40 mile mark.
So I had to google 'FNRttC'

One things led to another........
I'm currently considering a 210km (130 mile) audax