Adult entry is from 17 years of age, I take it your starting year 11 from the fact you have starting app in feb in the bottom box?? As said though the BMI standards arent any different on upper limits only slightly different on lower limits of BMI for JE. If your around 27 or above on BMI then it doesnt matter if your JE or SE entry you need to lose some weight. Speak to the ACIO who can have a better idea when they can see all the facts better but from what youve mentioned get into the correct BMI requirement.
The only thing I would point out what ever you decide to do and that was your final comment.
"I don't want to lose muscle weight, I mean, who wants to do that lol hard work, for nothing"
Its going to be extremely hard work to get to the required fitness, maturity and confidence levels firstly to pass ADSC and then to pass Basic training so if you need to be in the right frame of mind from the start.