Getting to the Century level

you have plenty of time to train for it.  I agree with the previous poster in trying to get at least one ride in the 65 to 70 mile range.  Also try to get in a couple of shorter riders during the week as you train.

You do want to review the course - is it hilly?   If it is then if you want to finish with some energy left in the tank, get some hill work in prior to the ride.  On your longer weekend rides be sure to fuel/eat during the rides so you can get use to your stomach digesting while riding.

No need to do 100mi as your long ride before your event.  As IC said, if you can do 60-70 without dying that should be fine by event day.  Get in as much saddle time training as you can 'cause ~6+hrs has a way of causing rump aches.  Work out pacing, hydration & fueling plan.  Dehydration in Aug is not fun.  Lighten up your riding 7-10 days pre-event so you're legs are fresh at the start.  Go easy for 1st 20+mi to get in rhythm.  I prefer not to stop for long at the aid stations- just grab some calories & refill the water bottles (& make a nature stop if needed).  Stop too long & you have to get warmed up again.  Don't be afraid to ask advice.  Most centuries are supportive, esp if other riders know you're going for your 1st. 

Good luck & have fun!!!

Great - thanks for the advice.  I knew there was a point, short of 100 miles, wherein the training was sufficient to do the ride ... I was just not sure where.  Obviously there's the basic need to get the time in the saddle prior to, but during the ride - the need to conserve energy and refuel is key; i.e. one should not go out too fast and wind up bonking with 20miles left

The event is this one in southern Virginia ... lots of rolling hills, beautiful countryside and a memorial to a really cool guy.

http://theartie.com/about-artie

Agree that getting a nutrition plan in-place is important.   Assume that this is some sort of group event with food stops, sag wagon etc.?

You can certainly do this. It takes longer than a marathon, but it's a lot more doable. You need:

(i) build up to being able to ride 70-80 miles. If you can do that, you're golden
(ii) practice eating during the ride, either at stops or while in motion. For biking it's not rocket science, as you digest fairly easily, but many of us still find that it takes a little practice. Anything beyond about 300 cal/hour is probably more than your body can digest.
(iii) especially for August, hydration and electrolytes are important: you don't want to cramp at mile 85
(iv) simply getting out and doing long rides will toughen up your butt, neck/back, hands, or whatever other parts tend to get sore from just being out there for so long
(v) if your century has hills and they're not part of your regular biking diet, start to include them in your rides

Enjoy. 

Learn what kind of things you like to consume on the bike. I'm doing my first century in 2 weeks, and this past weekend did a long ride of 64 miles. In the past I had been going out with a bottle of malto and a bottle of gatorade. I knew this week I would need more so I packed some fig newtons. I planned to drink my malto and gatorade and then eat a cookie every hour. I then learned once I got out there in the heat that I had absolutely no desire to eat solids and all I wanted was liquid calories. So now I've learned that I shouldn't rely on solids for nutrition and will probably be getting my calories from liquids. 

I'm not sure how good this formula is, but I used the formula provided in the article to estimate how much I should be taking in over the entire ride. I've been feeling pretty good though at the levels recommended by this formula. 

http://www.active.com/cycling/Articles/Determine_your_century_nutrition_plan.htm

Correct ... this ride has rest stops every 20 miles and SAG supported.  I've not done the ride but my son-in-law and parent-in-law rode it last year and enjoyed it immensely.  It's a well supported race.

40 miles now and you have until August?  You're golden. Unless you're doing something like Brasstown (14kft. of climbing) or something else on the slightly insane side.

I would definitely need more than that. Just did a 64 miler last Sunday that could be described as rolling hills. I'm a slower rider so it took me about 4 hours and 15 minutes. It was in the low-mid 80s for the entire ride. I ended up taking in right around 800 calories of malto and gatorade which was about 65-70z of liquids. I could have definitely used probably another 100 calories or so and another 25oz of liquids. 

IMO, the right pressure it makes ALL the difference in avoiding that nasty road vibration.

I agree with the previous posting where they mention getting your mileage up to 65-70 mile range on your long rides.  During the week, you don't need to ride as far, but it is important that you work on intervals (burst of speed for a certain time or distance, then back off, repeat).  Intervals are completed on flat terrain.   In addition to intervals, you need a training day dedicated to hill repeats.  Find a good, steady hill where you can remain in your seat, but continue a steady climb for 5-15 minutes.  Repeat 5 times or...   It's important that you have a good warmup leading up to intervals or hill repeat days.  My typical training week looked like this:

Monday - easy spin, short distance

Tuesday - 25 - 30 miles with intervals

Thursday - 25-30 miles with hill repeats

Saturday - long ride 50- 75 miles

You don't necessarily need to ride a 100 miles prior to your century.  If you can do 75 comfortably, then you can do 100. 

Good luck and have fun.