The ACF isn't part of the Army. Okay, there are uniforms, traditions and badges of rank, but all adults in the ACF are essentially youth workers. And don't worry, there's no danger of military call-up.
There are two types of adult instructors - click to see the how you can move up the ranks:
Adult instructors who hold "non-commissioned officer" army ranks. On appointment you will be a Sergeant Instructor and there exists the opportunity to rise to Regimental Sergeant Major Instructor (RSMI). Along the way you are likely to be a detachment instructor and later a detachment commander. From there you will likely take responsibility for a number of detachments as a Company Sergeant Major before rising to the rank of RSMI where you will be the senior non-commissioned rank in your county!
ACF Officers hold a Special Territorial Army Commission. On successful completion of an officer selection board you will gain the rank of Second Lieutenant. At this stage you're likely to be responsible for running your own cadet detachment in your local town. Progression is then available through the ranks of Lieutenant, Captain, Major, Lieutenant Colonel and Colonel. Along the way you will likely take on a number of roles the more senior you become. This may be running the training for a number of detachments in your area, or being entirely responsible for the running of those detachments. You may take on a specialist role for your county such as running adventurous training or shooting. If you have what it takes then you could end up as Commandant for the entire county in the rank of Colonel!
Adult instructors of any rank may be considered for a commission at any time in their ACF service.