Sassy
I can see why it is confusing.
Warfare and Logistics Officers can apply to join as 6th formers, because their A Levels allow them to fulfil the educational requirement (UCAS Points) and they can then start training after leaving school. Applicants for 6th Form scholarships apply either before or during their 6th form studies - some of them join after school, some go on to University; a proportion of the ones who go on to University apply for sponsorship there as well.
My understanding of the rules for the Medical Cadetship is that it is applied for during a medical student's 2nd year of studies at medical school. The Cadetship is then paid during the next 3 years.
It occurs to me that there may be some students who hope to become Medical Officers and apply for the Medical Cadetship at Medical School who also apply for the 6th Form Scholarships before going to University.
As it is quite a complex matter and I would want you to have the best advice, I would suggest that you speak to the Navy's specialist medical recruiters in Portsmouth - there is a small team there who deal exclusively with applicants for Medical, Dental and Nursing.
Quite a few questions about joining the Royal Navy come up on the NavyNet website and some of them are about joining as a Medical Cadet.
This is a link to one of those threads. In it, Ninja Stoker, who was a Royal Navy Careers Advisor at the time, gives the poster the number for the specialist medical recruiters in Portsmouth. Have a look at the thread and give the number he gives a call - it's the best thing to do, as the specialist team will know what the current situation is as far as the Cadetship and potential sponsorship at 6th form level for potential Medical Officers is concerned.
https://www.navy-net.co.uk/community/threads/medical-officer-specialty-training.81681/#post-1263914Something I would recommend is that you go to a Medical School which allows you to join a University Royal Naval Unit.
https://www.royalnavy.mod.uk/our-organisation/bases-and-stations/training-establishments/university-royal-naval-unitsI thought that you might like this link too:
http://www.theadventuremedic.com/features/life-royal-navy-doctor/