I think that anybody should do their PPL first, before committing to commercial training.
It will tell you if you have the aptitude and motivation to be a pilot - no amount of interviews and "aptitude tests" will tell you that as well as a PPL course with a good school and instructor.
If you turn out not to have the aptitude, or not to enjoy it - then £6450 was a very cheap lesson compared to the cost of doing your fATPL, in terms of both time and money. If you turn out to be good at it, and love it - then the cost is still trivial compared to what you'll have to spend later, plus you'll hit the commercial courses from a much better starting point. You'll also have a much better grasp of the PPL process if you become a flying instructor - as a great many do on their way to more lucrative flying jobs.
G