Question for long distance cyclists

Make sure you break the saddle in properly before the event aswell or use your old saddle

It's plenty of time, and being a charity ride, I assume the pace is whatever you want it to be and it's probably fairly well supported (food/drink/bathroom stops along the way). That means the biggest thing you have to worry about is the 5-6 hours it's going to take you to complete. Get more time in the saddle, get used to being on the bike for longer stretches of time. Don't worry so much about distance or speed at this point, just focus on time in the saddle for now.

I'd agree - even if you only train to about 50 miles, you should be fine (assuming you feel okay at 50 miles). When I do century rides, I tend to train just to about 70 or so miles and just jump up to 100 on the day of the event. You have plenty of time so I would just add in one longer ride per week if you can. The bigger thing that I train for is if you're riding with a group of friends, get used to using a paceline and calling out road hazards and such. If you're just riding on your own, then maybe just add on another 5 miles a week or so to build up to longer rides.

Have fun!

The best training is just time in the saddle. Start increasing your weekly distance and you will be fine by September.
Taking a few detours on your daily ride is an easy way to fit in more training.

Bumping up your (weekly) longer rides by 10% at a time would be an easy progression.
Good cycling shorts, comfortable saddle and chamois cream will get you through!

Saddle the time, saddle time saddle time. I prefer a good saddle with a cutout. And good biking shorts. Hydrate like mad a day or 2 prior, during the ride, and that night.

Lots of great advice. The only thing I would add is that in addition to good biking shorts, pick up some chamois cream. The more time you send in the saddle, the more likely it will be that you will get some skin irritation. You will quickly figure out if you have some spots that are more easily irritated. So a quick coat of the cream on those areas of the chamois pad will make a big difference. When I was younger, I never needed to use anything. But as I have gotten older, this has become a necessity, especially earlier in the season when the skin hasn't toughened up yet.

Also - regarding food on the ride:

It's always nice on supported event rides like that that they provide food, but make sure you're only eating things that you know work for you. I have a pretty iron stomach for these things, but have friends who can't touch banana while they ride or they are just doubled over in pain. Wouldn't be good to discover that in the middle of an event.

If your event is anything like the ones I've done they usually have fresh fruit (bananas/oranges are very common), bars and cookies, peanut butter, trail mix, and energy drink stuff (usually by whoever is sponsoring the event) with Subway sandwiches at a lunch stop. If you've got any food sensitivities, it's worth just carrying your own food - I don't eat sugar or grains, etc. so I personally stick to the fruit and bring my own raw nuts and dates to snack on. You can also get electrolyte tablets that are easy to carry with you if you have any concerns about what's in the drinks that are provided other than water.

And regardless of what you decide to eat on the ride - DO EAT AND DRINK. On the shorter rides you're on now, you don't really need much, if anything. Once you're out on your bike for hours, if you wait until you feel hungry/thirsty, you're going to run into problems. I have a clock on my bike computer and keep an eye on the time and make sure I eat and drink regularly. You can overdo it too, but you're better off to have small snacks and drinks frequently than to try to catch up if you get behind.

As a triathlete and avid cyclist I feel the most important thing about your distance event for you will be comfort. Getting a proper fit on the bike will be critical, pay an established bike shop to have your bike adjusted to you (and the bike inspected). Your saddle height, saddle position fore/aft/angle, bar reach, and height. Spend the money to get (at minimum) mid grade cycling shorts or above (they are expensive but worth every penny once you are in the saddle over an hour, I also second chamois cream). Bring plenty of food/drink and stay hydrated and full of good energy foods. Just keep riding every chance you get up to the event, with the SAG stops and general pace of the ride, it will feel more like 7, 10 mile rides..but if you are uncomfortable, thirsty and tired from hunger, it will feel like 10, 70 mile rides.....

^^^^ Pretty much nails it.........a good pair of biking shorts makes a world of difference and a properly fitted bike is both more comfortable and mechanically efficient.

You may also want to invest in a biking jersey if you don't already own one (the charity ride I do each year gives a freebie for each ride) - they have pockets in the back that are perfect for carrying snacks, your cell phone etc etc.

Another handy item to get is a RoadID. We never like to anticipate having problems but in the event of an accident wallets can go flying - with a RoadID (I use the bracelet one, some people like the one that goes on their shoelaces) you can have basic contact info, blood type, allergies etc - one of those things you hope you never have to use.

Plenty of time! Not sure what kind of bike you are buying, but I recommend that you get a road bike. Your commutes to work are a good base for you, now add in a weekend ride of increasing length. Start off by increasing 5 miles a week on that weekend ride. Make sure test out what you will be eating, these rides always have rest stops with food ... in general it is peanut butter & jelly sandwiches, bananas, apples, and nuts. Some will add in granola bars, chips, and candy. If these types of things aren't enough to keep you going pack something for yourself. I like hammer gel and buy it in bulk and carry a couple of flasks on long rides (this is a long ride).

Saddle is important and personal, what works for one person will not necessarily work for another. I must say don't even try that noseless saddle, you loose a lot of control without that nose. I myself like the Terry Butterfly saddle, I know women who hate it, and others swear by the Brooks saddle. One thing to remember the softer the saddle the more it is going to hurt you after 15 miles. Soft works for about 10 - 20 miles and then it kills you (the cushion compresses and then you are really kind of sitting on the frame ... ouch!). I like the split too. I used a Bontraeger Women's saddle for years and it was great, I wore it out and thought I would try the Terry because it got such good reviews and I like it too. I do not like Italia saddle too hard never could get it broke in. But who knows it might be perfect for you. Good luck and have fun.

If you want a structured training plan you could check out the beginner / intermediate training plans found here:

http://www.bhf.org.uk/get-involved/events/training/cycling/beginners-training-schedule.aspx

You have more than enough time to prepare.