You are going to be GREAT!!! Congratulations on your decision to go back. I'm not sure how long it's been since you were in school, but if it's any consolation my mom went through a pretty nasty divorce, and when things had settled down she decided it was time to start taking care of herself for a change ... starting by going to college for the first time at the age of 53. She was really focused and had a really good idea of exactly where she wanted her degree to take her, (which she might not have had when she was younger) and graduated with almost a 4.0.
I can sympathize with you as well ... I've been out of school for a few years (and also feel OLD!) and in 2 weeks am moving to PA to start a PhD. I am terrified. Scared that I won't be smart enough, disciplined enough, etc. But I refuse to let those feelings control me. Let's just give it our best shot and see where we end up!
I wish you the best of luck ... if you ever need anyone to commiserate with, you can count on me.
