Promotion

So I'm 49 years old. I've been working in the same department as a manager since 1998. Transferring to many stores along the way. So I was approached last week as someone is retiring and was asked to step up and become an assistant to the store manager.
I'm scared. I'm worried. I just don't know if I can do a good job. I have no knowledge of what goes on in some parts. Some I do because of my previous experience leading people along the way. I am always the person people call when they need advice or help. Now this promotion is a lot of responsibility and I need a response by Thursday. The money doesn't interest me. I know I'm hard on myself and I think that's what worries me. Am I nuts for taking this on?

I need some opinions.