Everything so far is good advice. I’ve been riding seriously for 12 years, each year I seem to up the anny for distance. Now I’m a member of a small in group in our cycling club called the ultra-milers. Each of our rides is 80 to 110 miles in length on hilly terrain.
Get a professional bike. Be sure and hydrate even when you’re not thirsty. Most important, don’t forget to eat. When riding 100 plus miles forget the power bars, etc. Eat real food, comfort food like sandwiches, pizza, fruits. You even need a little fat to help keep going. Don’t be afraid of it, you’re going to burn in up.
The more you ride the more your body will get acclimated to the longer distances; it just takes time and the willingness to put in the miles.
H.R.