1) 16 to go solo, 17 to do the Skill Test (you need to pass obviously to get the PPL) (plus 7 multi choice exams, and a Radio exam/test)
2) 45, of which 25 must be dual (i.e. with instructor), and 10 solo
3) Anywhere between £6-15k+ depending where you train, and how long it takes you (45 hours is the minimum, may people take more)
4) Best to ask in the Wannabes forums, but it's few if any, and the chances of getting in are so low as to be zero. Either go modular (do it in bits), which will cost you about £40-60k, or £100k+ for integrated (do it all at one school on one course).