Gazzad,
You're correct when you say that your parent unit cannot stop your application but that will only get you as far as selection. Not much you can do about the medical but try to find out as much as you can about the AAC and the army in general, you will be probed on the interview and during the selection tests as to your knowledge about how the army works.
I came from the infantry and had a lot of help from some of my Bn with publications that could expand my overall knowledge of the army.
As has been said before, don't take too much notice of the naysayers, it's probably down to lack of drive and pure jealousy.
Have a go! The worst that can happen is that you will still be doing the job you're doing now and it might just change your whole life.
Good luck.