Reading Half Marathon in aid of National Autistic Society... Should I do it?

I am considering entering the Reading Half Marathon to raise money for the National Autistic Society who support so many people living with autism and their families. Of course I want to raise money for the charity but let's face it, I'm hardly at the peak of physical fitness. I will need to do lots and lots of training, as this would be running 13 miles.

If anybody who reads this has any training tips it would be greatly appreciated. If I successfully complete this I would feel so proud of myself.

I am spontaneous and a bit crazy so yes... I will probably go ahead and do this!