yeah thats right you can join either at 16, theyll be both the same though that you have to be 18+ to be deployed on a tour, and dont alot of 16 year olds that join the army go to that army college for a while before they start training etc?! (cant remember what its called!)
Just to clarify (& apologies if it appears I'm being pedantic)
You can apply for all 3 services from the age of 15 years & 9 months- Yes, whilst still in Year 11, with parental consent, you may undergo the complete selection process before you actually leave school.
You may not join until the completion of your academic year, after the last GCSE has been taken in the June of that year. This applies even if you consider yourself to have left school/opted out/or are not sitting any GCSE's.
As stated, you cannot be deployed operationally until 18 with the Corps. I have heard of someone under 18 being deployed with the RAF Regiment, but it is not policy to deploy under 18. For Army, same at the Corps, you will not be operationally deployed until 18- soldiers usually go to Bassingbourn or Harrogate.