Welcome to TE!!
Some good advice has been given so far. I think 35 miles is MORE than doable by October!!

Here's a training schedule I found on the Susan G. Komen Ride for the Cure website:
http://www.komenaspen.org/ride/alder_train.html

Depending on how you feel as your training progresses, I can imagine you could do the metric century by October- that's plenty of time for training.

Here's Komen's century training schedule:
http://www.komenaspen.org/ride/sched.html

If you do the two training programs back to back, that's 18 weeks of training leading up to a century in October. See what's doable for you.

Good luck, and keep us posted on your progress.