As an abject failure at every aspect of life I would definitely jump at the chance.
Had I lived a life worth living I could see the downsides, like how much a 12 year old's biochemistry conflicts with an adult mans mind.
As such I certainly wouldn't have chosen 12 years old and I'm curious as to why you did?
I think 12 is a very appropriate age. It's generally seen as the last year of real childhood and innocence. Many of life's mistakes tend to start happening during people's teens. High school seems to be the start of the more indelible errors one makes. 12 gives a chance to nip those in the bud.