Your height is going to be something you'll have to overcome, but with practice you should be able to learn to fish. Your sense of balance is also going to be a factor.
On the Ride make sure to slide the seat all the way back and stand up there, not down in the footwells. When standing make sure to get your feet as wide apart as possible. There are generally two ways to stand on a kayak. One is to keep both legs slightly bent with your weight evenly distributed on both legs. The other is to apply a little more weight to one leg, which causes the kayak to list to that side but this causes the kayak to "lock" it's stability some. Let your hips absorb the rocking motion and keep your head level and over the centerline of the kayak. When standing try to keep a narrow field of vision (like 10 to 2). Your sense of balance will start to decline the further you turn your head around. Don't look straight up either, and keep a point of reference on the horizon or shoreline. With your height a stand assist strap would probably help.
Don't start fishing until you're comfortable standing up. When casting or setting the hook take it easy at first. Don't try to fling your bait a mile or do a "Bill Dance" hook set. After you get a feel for standing you then need to get a feel on how your body and kayak will react when going through the fishing motions. There's a lot of changing forces and momentum when you cast and set the hook that get amplified when your center of gravity is that far above the waterline.
"Water is life's matter and matrix, mother and medium. There is no life without water." -Albert Szent-Gyorgyi
"No man ever steps in the same river twice, for it's not the same river and he's not the same man." - Heraclitus