Carbonfiberboy 

I just read your Newbie thread, which I hadn't seen. I think you're on the wrong track in this thread, not that nutrition isn't important. So let's take nutrition first because it's simplest. Rules: Eat a high carb breakfast 3 (three) hours before your group or other long hard ride. I shoot for 400 calories total. Yeah, that's a lot. Then during the ride, eat small amounts, say at most 50 calories of carbs every 15' or 100 every 30' - experiment with different foods. You might be fine with half of those calories. And just keep it coming. With small amounts on a consistent schedule you won't spike and won't run out either. IME, glycemic index doesn't matter for foods eaten on the bike in small amounts. I ride with diabetics who eat like that, so experiment, see what feels good. So that part's actually easy. I set my Garmin to beep at me when I should fuel.

The harder part is building endurance. The only way to do that is to ride a lot. Gradually increase your weekly miles, no more than 5%/week, but be consistent. Ride your miles every week. I think it's easiest to do frequent say 20 mile rides and then a long ride on the weekend. Eventually make that 2 long rides on the weekend. A good goal is 150 miles a week. Of course more is better, but at ~150 miles/week, more miles start to have diminishing returns per mile. And not necessarily that many miles every week, but shoot for ~5000 miles/year. Depending on where you live, you'll probably do less in winter, but with an indoor trainer you'll keep up the consistent riding, just fewer weekly miles. It's a year-round sport.

In your Newbie thread, years were mentioned, and very true. It takes about 7 years to go from newbie to you're not going to get much stronger than this, that is if you keep up with the consistent riding. That 7 years seems a bit arbitrary and probably does vary with age and individual, but IME it's about right. It's a long term thing which demands a bit of dedication and a lot of consistency. If you keep it up, you'll find that you can ride a century on any given day, no problem.

Riding consistently, you'll notice that you can't ride hard every day. Most of your rides will have to be at a moderate pace or you won't recover and be able to do another one the next day or even 2 days out. That's a good thing. However, when I do full-gas weekend rides, I don't do anything for a day or 2 before the ride. Moderate rides shouldn't be so hard that you need to rest a day before the next one. That said, you can do other things and miss a day or even 2, no big thing, you just need to do your weekly miles, whatever that is..

Gradually building distance over time will change how your body stores and uses nutrients and not only that, you'll figure out your nutrition and hydration needs and all that. That'll all come over time as a result of riding more.