Shoulders.

My horse is a TB gelding and he has issue with jutting his shoulders out, my trainer told me that I can't do jumpers before I fix this, does anyone have ideas techniques?

Not sure I follow with what you mean by jutting his shoulders out. What exactly does your horse do?

When I turn him left he will stick out his shoulder so he basically drifts.

So you are saying under saddle he does not track correctly?

Not exactly, he is perfect tracking right but when I cut across the diagonal he sticks out his right shoulder so that he wont have to turn. At the walk he's fine but cantering and troting is when I have a problem

He's not working back to front. Sounds to me like you need to work with your trainer on getting your horse to accept the aids, work from his hind end through his back into the bridle. A headset without engagement will just lead to false framing and the horse can easily disconnect at the shoulder and "pop out" a shoulder and drift in the opposite direction you are asking him to move. That tells me that the horse is not moving properly engaged from his hind end.

Right but, he refuses to bend his head, and I can normally get him to engage, I just got him 2 months ago, and his previous owner rode him once a month, and he needs to be ridden 4-5 a week, all of tough my trainer has a book of exersizes that we work on and those have been making him engage its when I just do flat on the rail that he is bad. He's been getting better, as I have been riding him more than his previous.

As CJ has already stated, he's popping his shoulder - when they pop their shoulder, they are unbalanced.

Get your outside rein activated here. Your seat rides the hind end, your legs ride the ribs, and your reins ride the shoulders *not the face*. So when he pops his outside shoulder, get your outside rein on that shoulder to bring himself back under himself.

Ride inside leg, into outside rein.

I suggest you get into Dressage Lessons when you can :)

Or in simpler terms - your doors are fully closed. Outside Aids.

My trainer and I are working on that, we are "filling in the wholes" and its been helping, he is very quick and has alot of stamina which makes it hard to concentrait on more than stopping when needed.