When I 1st started riding regularly I would run out of gas at 20 miles. I didn't matter if I was riding 20 miles or 50 miles, I was always bonking at 20. I would then stop and take in some calories. I did this for a year before I figured out that I need to be fueling my body right from the start and very regularly on rides over 20 miles. Now 100 is achievable when my pockets are loaded up with gels and beans and bars. The occasional stop at a gas station for a donut doesn't hurt on a very long ride.
It just takes time to figure out what your body needs and what works for you. Good luck, and congrats on the accomplishment!

Congrats! Cherish those milestones. As pointed out above, they tend to get fewer and farther between.

I still remember my first 20 mile ride. I bragged about it to anyone who would listen for weeks. 40 took a while to work up to as well.

It's a big learning process. You'll learn where your feet, butt, hands, etc. are all most comfortable. You'll experiment with clothes, goo of all sorts, breathing, your position, your mindset, your diet and time management. You'll have to buy new belts, pants, t-shirts... Maybe even a new haircut.

You've crossed a threshold of sorts -- you've proven that you are not just looking to spin the pedals and wave at pedestrians on a boardwalk somewhere. You've proven that you are willing to suffer for speed, fitness, mile markers and round numbers that mean both everything and nothing at the same time. You're a cyclist. Welcome.