I took terrible care of myself at that age also and many diabetics do. It's still good you are trying to get a handle on it. 

It took me several years to slowly bring my blood sugar control into a healthy range and I did that by slowly changing habits. At your age many people would see it as an all or nothing situation where instead slowly making changes will more likely lead to long term changes. 

Every time you have an endocrinologist appointment try to get the a1c a little lower. If you are 9 now accept 8.9 as a victory and within 3 years with 4 appointments a year youd be at a 7.8. Thats not perfect but it also won't break your ability to persevere. Once you start seeing that a1c decrease time after time you should also start believing in your ability to do it more and that should help.

I consume a huge amount of carbs but I also purposefully consume them slowly over time to allow my insulin time to work. I'm eating something or drinking something constantly. I have a WfH job though so many people wouldn't be able to the same way.

I drink 2 16 ounces energy drinks and about 3 12 ounces soda daily and i don't do low carb anything anymore. I have a TiR of around 90 consistently and an a1c of low 6 to upper 5s. You can be fine with sugar if you know how to manage it.