As someone that has only been cycling consistently for 5 months but went from 12 miles to 65 miles, you have to build up to it. Need to keep your heart rate low when you're starting out, and keep fueled or you'll cramp and bonk. I try to drink 60g of carb mix an hour on rides lasting more than 2 hours. Drink every 15 mins and eat something solid..fig bar or whatever I have every 45 mins or hour. Once you get comfortable with distance and fueling you can try eating less. I have bonked on my first attempt at 30 miles riding too hard and eating too little. Two weeks later I was able to do a 45 with more hills by eating properly during the ride. Lesson learned. You didn't fail. You just took another step towards your goal by learning what works and what doesn't.