The best place to look for information is here:
http://www.caa.co.uk/srg/licensing/fcl/document.asp
especially the "LASORS 2003 - LAS section" which will give you all the requirements in more detail than you ever wanted
The fATPL does require more flying, as you need to add an Instrument Rating to the CPL (done with ATPL theory exams of course). The airlines will expect the IR to be done on a multi-engined aeroplane, so you'll need the MEP rating too. Think I've got that right, although someone is bound to correct me...
The Wannabes forum is probably the best place to look for more information on age-related issues. I'm sure it has been done by people older than you, but it is less common.