Hi there! and welcome to the club........
Like the previous posters mention, build up to about 80% of your target distance in training rides. Increase your weekly TIME (not distance) on the bike by 10% every week for three weeks then cut back to 50% of the 3rd week's total training time on the 4th week. This is your recovery week - take it easy with no hard efforts, just go out ''for a spin''.
Break the week up into hour to hour and a half rides during the week with your longer ride on the weekend - 2hrs+ and make sure you have 2 clear days of no exercise. Recovery is vitally important, though you're 15 years younger than me, you lucky devil and so you'll recover pretty quickly.
week 5 is 10% longer time on bike than week 3 and so on through week 6 and 7. Week 8 is 50% of week 7 exercise time.
Right. A couple of months of that and your distances on the weekend should have come up nicely. 2hrs will have become 5hrs or so, with a bit of luck.
Plan circular routes and pay attention to the contour lines on the map. Close together means steep! Pay attention to wind speed and direction. I use
www.xcweather.co.uk
Make sure the wind will be behind you on the way home and also plan in an 'escape route' to shorten your ride should something go wrong like a mechanical issue.
Climbing hills. It's extremely useful to determine your aerobic/anaerobic threshold heart rate. Get a heart rate monitor/computer and learn to use it. On a day when you are feeling fresh and strong, warm up slowly for 15 mins - reset your heart monitor to zero and then ride a hard, best effort time trial for 30 minutes.
When the legs fill with lactate, back off the power only enough to enable you to keep going. It's not a flat out sprint, we need to find the highest heart rate you can maintain for a decent length of time. You could do an hour for greater accuracy, but if you've never done an ''Hour'' before it will prove very tough indeed.
The average heart rate on your monitor for that test will be within +/- 3 beats per minute of your anaerobic threshold. This figure (mine is currently 151bpm) is the rate you should maintain on climbs. If you repeatedly exceed this, you will tire yourself out prematurely and will struggle on the final climbs of your event. During training, however, push on up to your threshold and stay within +/- 5bpm of it on days you feel good. This will train your body to withstand lactic acid and cope with it more effectively. This time last year, mine was 136.............
On climbs, keep pushing on over the top and click up the gears on the decent, whilst applying just enough power to move up through the gears smoothly. You will recover well enough and help your body to remove the excess lactate from the muscles. At the foot of the decent, you will be moving much faster than if you merely freewheeled down, you will have retained momentum and be able to maintain a much higher cruising speed than normal for a short while.
Naturally, if you're going really fast, you should concentrate on maintaining control of your bike and shouting YEEE-HA! as loud as you can. This is very important.
On the flat sections, roll along at 10% under your threshold HR. You'll be able to maintain this fairly brisk pace for a very long time and cover a great deal of ground surprisingly quickly.
A final word on nutrition. It's a good idea to use an electrolyte sports drink like SIS Go during your rides. About an 800ml bottle per hour. On longer rides, eat also, little but often as soon as you get on the bike - Torq gels(delicious) and bars, Mule bars, Hi5 gels and the old favourite, Fig Rolls all work well for me. You're looking for a mix of complex carbs/simple sugars with a bit of protein but low fat. For 2hr+ rides, a sports drink that I've found to be particularly effective is Hi5 4:1 Energy Source. A couple of my pals use SIS PSP22 and swear by it, but it sits really heavily on my stomach and makes me want to chunder. It's a good idea to try as many kinds of sports nutrition products as you can during training so you know what products will work for you on the big day and you won't risk throwing up.
That's about as much as I can type at the mo'.
Best of Luck!