I always thought the OU scheme was designed so that you started studying AFTER flying training, the point being to get young guys like yourself in to the service, get your wings and onto the front line, and then supporting you through further education.
It doesn't make much sense to me to force you to study for a degree at the same time as conducting full time flying training. Mind you, this is the RAF we are talking about....
Perhaps an option is to apply now for Direct Entry, but if unsuccessful go to Uni and apply for sponsorship after the required period. If successful second time round, you will then be given an offer of service to enter IOT when you graduate (assuming you are awarded a bursary), which may get round the age limitations.
If Mike Jenvey is lurking here, maybe he could clarify whether sponsorship can be awarded to a guy that will be over 23 at graduation, but has been successful at OASC before 23?
Damn university types always manage to make things complicated.
