I know you don't want to hear it, but it doesn't sound like the best idea in the world, as others have said already. (I personally advise against it until you're older and find a respectable tattooist)
But... since none of us can stop you, and you sound like you've got your mind made up, let me just say this and please, for your own sake, Listen:
This tattooist, will be doing it illegally, which isn't very responsible of him. This could also mean that he won't be using proper equiptment.
MAKE SURE HE USES BRAND NEW, STERILE NEEDLES & EQUIPTMENT! Diseases can very easily be spread through tattooing without sterile needles and such. They can also cause serious infection. So if you're fully determined to do this at least be safe/smart about it. Okay?
Lecture over!
Take care.