What background do I need to have before starting Arduino?
I am a Electrical technician and bought the starter kit from the Arduino team for my 13 year old son. My plan was to try the kit to teach my son about electronics. 

The end result is that he is the one showing me new stuff. 

In my opinion, you do not need any special background before starting with Arduino. You should have a interest in learning something new, and in learning about electronics. To get started, buy a tutorial book and a starter kit. (Many starter-kits comes with a tutorial book) When you have gone through the book, you will have some basic knowledge and a base to continue learning from. 

Good luck