Almost everyone should be able to hit depth in a squat, tall and lanky guys with longer femurs just have to squat a bit differently from the shorter and stockier builds.
I'm 6'3 btw, with long femurs and thought I couldn't hit proper depth for a long time. Now I can back squat ATG without rounding the back. Its just about finding a good squatting style for your proportions.
Work on you mobility if you're not flexible. As a tall guy with longer femurs, you need good ankle dorsiflexion, lower back flexibility and to be able to open up your hips and shove the knees out to the sides. You should try to take a wider stance and let the knees travel more forward over the toes. Sitting far back in the squat does not work as well for those with longer femurs and will often lead to butt wink (lower back rounding).