Quite a few people get a bike for a charity ride, do a couple of training rides then head out for a tough endurance event. The next day it hurts and they get put off cycling.
A sensible approach is to toughen your body up gradually to the new stresses of cycling. If you are a fit athlete you can convert to cycling long distances in a couple of weeks. If you are not an athlete you have to convert to cycling AND get fit. This is going to take close to three months of regular riding.
A reasonably fit (but non athletic) rider who is used to regular riding can do a 90 mile ride and still feel like getting on the bike the next day.
You should try to ride every day. Use the bike for comuting/shopping/errands etc as well as training rides, to get more saddle time.
Training rides should be a min of 1 hour.
Get some longer rides in, at least 50 miles.