Age limits are allowed if training costs are involved that a company cannot get a return on over the period of employment. It is fairly unique to aviation as there is, unless I am mistaken, an upper age limit for flying at 65 years, therefore an airline could prove that the costs involved in training a 60+ year-old would not be recouped. i.e. there would be no return on investment. As BA are paying for JOC and TR (and they could argue they are paying for the CPL/IR training as it is "sponsored", even though in reality it is not) they are not doing anything illegal.
Would anyone above the age limit would want to apply anyway? The upper age limit is probably a moot point.
The competition between the FTOs is a very interesting element to this scheme, is it just me or is FTE by far the cheapest one? The other schools do not include living costs and CTC charge an additional £3,300 for training equipment. OAA and CTC charge for selection - I am not sure if FTE do or not.