Just wanted to give you my support, as well. Age really IS just a number.
There are people in my class ranging from straight out of high school to mid-40s. I will be 33 when I graduate in April, and I can tell you that going back to school is the best thing I ever did for myself.
The way I looked at it when I was contemplating nursing school was this: in 4 years, I'd be 33 years old...regardless of my career or choices. So did I want to be 33 and in my old office job that I hated? Or 33 and embarking on a career in nursing, which I had always wanted?
Stick with it, and you won't regret it. Best of luck! And remember that when your sister isn't being forthcoming with her help as far as different classes and such, you can always come to this wonderful site and many people will have been through those same types of classes and will be able to give you advice.