I can't say if the AAC Aircrew aptitude tests are the same as those for the RAF Officer and Aircrew aptitude tests, but I'd imagine they are close.
I attended in November 2002, so I may have forgotten some stuff, or indeed the tests may have been updated. You're right in that it was still PC based, however the actual pilot (i.e. joystick and rudder) portion of the test is actually a very short segment of the overall test designed to gauge your suitability for all roles, flight ops, pilot, supply, admin, in order to make it fair all applicants do the same tests.
I can't remember in what order the tests come, the pilot section is based on dots - white dot in the centre of the screen, is moved by the computer and you have to return it to the centre and keep it there as much as possible. Another is a vertical stream of red dots, idea being to hit the middle of as many red dots as possible with your white dot - if you pick a stream which peters out you lose out. There is a series of tests on attitude, pictures of an aircraft on screen in a certain attitude, you have to use a multiple choice display and decide which instruments are correctly displayed for that attitude and direction etc. Mental arithmetic features highly, I'd advise plenty of practice, you are only allowed a pencil and paper for one set of time/distance calculations, this then gets taken away. Obviously multi-tasking is important, the ability to perform mental arithmetic and remembering sequences of letters whilst keeping on top of little coloured triangles moving left to right across the screen and hitting a button at just the right time comes in really useful
. However, like I said, not all tests are relevant for the position applied for, some are related to pilot skills, some not.
To be perfectly honest, if you play enough computer games (flight sims or just anything with a joystick) it'll become easier to do the piloting part, practice the sums and do a few IQ tests online to get an idea of what they're like, it's not too bad although it is mentally draining doing it all in one morning - about 4 hours I think.
I hope some of this is of use, if you want any more info feel free to PM me, I'll see if I can dig up more info at home. Best of luck to your son.