Following on from the above:
Costs vary depending where you live, up by me, it's around £180 per hour for example - expensive, but it's cheaper elsewhere. You *can* train abroad on a "compact" course if that suits you for around £5k all in, but that's up to personal preference.
The most useful document for you to look at right now is LASORS:
http://www.caa.co.uk/docs/33/LASORS_07.pdf (see Section C1) it contains everything you need to know about the PPL issue. Most of the below is taken from that.
You can't be issued with the PPL licence until you are 17, but you can train towards it from 14 onwards (including the skills test).
Minimum experience to get the licence issued is 45 hours of which 25 must be dual instructed, 10 must be solo and include a cross country (xc for short) flight of at least 150nm with landings at 2 different aerodromes as the departure one.
There are 7 exams - all multi-choice and a practical RT (Radio Telephony) exam which may be done as part of your skills test rather than an formal exam.
Air Law (one of the more boring exams) is usually required before soloing in the UK (not legally, but generally accepted thats the case).
The standard texts for the books are the Trevor Thom series or Jeremy Pratt. Each to their own - Pratt is a bit more wordy, but I personally preferred them to the Thoms. Any flight equipment shop (Transair et al) and probably your club will have them.
You will need to hold a Class 2 Medical certificate (for the licence issue - but not during training). This consists mainly of a vision/hearing test, finger prick blood test and an ECG (machine that goes ping). If you have any major health issues, are colour blind or have bad vision, seek advice - it will curtail your activities. If you're considering going commercial in a few years, you'll need a Class 1 - even stricter. The Class 2 will cost you around £120-200 to get, and its renewed on a 5 year basis until you're older when it drops to 2 years (I think - might be wrong on the 5 year front).
Good advice is to NEVER pay for anything up front (Flying Schools have a habit of going pop), and to get the medical first rather than later.
Once you get the poo coloured licence, you need to do 12 hours in the second year to keep it valid including an hour with an instructor, and it lasts for 5 years.
Currency is key - if you can't fly at least twice a month when learning, you should consider waiting, save your money, and have a consolidated go at it over the course of a couple of months later on (or do a residential/4/5week course).
Flying every day/couple of days does wonders for your ability whereas trying to pick up where you left off every 5-6 weeks is a nightmare. Bear in mind the UK weather does not lend itself to flying training.
And most of all, enjoy it!
edited the bit about the skills test/licence issue at 17 for posterity!