How old do you have to be? How much does it cost? Do they ever fail like has anything bad happened that they messed up?

Many surgeons will require patients to be 18 for surgery, but there are also other surgeons who follow WPATH standards and will operate on minors with parental consent.

You can find a summary of costs, organized by surgeon, here:
http://www.topsurgery.net/costs/

Revisions are quite common, but serious complications are pretty rare.

Hope this helps!