Well, in many ways this is not unusual. Kids with ADHD can be two or more years behaviorally behind their peers. Part of this is simply because they lack the impulse filters their peers have. Thus, while most kids have learned to stifle there impulses better as they age - ADHD kids lack the ability to do so. Medication should help this. But.....if the meds aren't correctly prescribed....too little or too much, the help will not be as great as it should be.
And medication is not the only thing going on, but since it is the easiest to deal with. Lets do that. Most extended release should work for about 8 hours, unless its Vyvanse which can go 12 hours. You need to talk to his teachers and see if he appears to lose focus as the day progresses, or if he reverts to an immature behavior as the day goes on. If he does, then you need to let his doctor know as his meds should probably be evaluated. And, of course, how he treats you at home might be a sign the meds are wearing off. If he is a smart kid, homework may not yet be a problem - but if he is beginning to resist it or if it is taking forever to do - that is another sign that his meds need to be evaluated.
I am very pleased to hear that he has therapy. Many parents will not do that - even though all studies show that therapy and medication is the most productive way to help the child. Unfortunately, parents also need training in how to work with their child. It is a whole different ball game. I have always advocated the parents sitting in during part of the therapy so they can better understand how to help there kid.
You say he doesn't listen. That is very common ADHD behavior. Unless, you can get him looking straight into your eyes (and even that may not work) his mind is somewhere else. And talking over you is because he is not listening to you. I mean it is not you! These are very common ADHD problems. And they can be addressed in ways besides meds.
Fortunately, there are some excellent online resources.
A good starting point is here - https://www.additudemag.com/behavior-therapy-it-works/
This is a really good overall look - https://www.helpguide.org/articles/add-adhd/when-your-child-has-attention-deficit-disorder-adhd.htm
And this has some specific ideas - https://www.additudemag.com/behavior-punishment-parenting-child-with-adhd/?utm_source=eletter&utm_medium=email&utm_campaign=april&mc_cid=575b694d3e&mc_eid=34d357d554
And all of these links have many other resources listed with them. I hope these help. And really this is just the starting point. If you can get better information on how to deal with these adhd behaviors, things will get better. I have a ton of links I didn't send because I did not want to burn you out. So if you have any specific questions, please feel free to ask. Best wishes.
I just came across this link and thought of you guys. Looks like it might be helpful.