Big Mister
I did CPL/IR/ME at 43 myself, in 1999/2000, and can highly recommend it. They are now busier than ever and you will need to book a place months in advance, also its probably more expensive than other schools, but it still is a fantastic place to learn and fly. They do take on former students as instructors, you should speak to the CFI, Steve Goodrick, or Frik Schoombee.
Another school with good reputation is Blue Chip aviation in Pretoria. They also do a package for CPL/IR/ME/instructor rating, with a chance of work afterwards.
As for converting your license, George has summed it up nicely, first priority should be to get your JAA ATPL exams passed. Sooner you start, the better, you should do them distance learning whilst doing the flying training in SA as they are also good preparation for the SA CPL exams!
If you have a full ICAO ATPL with multi-pilot type rating (multi-pilot according to the manufacturer, ie 737/A320, not Beech 200!) and you have min. 500 hours on type, you can do an ATPL flight test on a simulator with a JAR examiner to convert your ATPL. This also exempts you from the MCC course. Not applicable to you yet, do the exams first
Good luck
JD