Yep, you need a longer bow for that long a draw. The best way to learn to shoot well would be to get an old target recurve from one of the classified sites or ****. There are lots of them available in 69 or 70 inches and draw weights around 35 pounds at 28 inches. That would be maybe 45 pounds for you. Might as well get a nice old Bear target recurve to match your Grizz.
Second, learn the deep hook hold, in or beyond the crease of your middle finger. I go beyond. Tabs work well for this. It is smoother and easier on the fingers than the finger tip hold.
Once you have gotten good, you may well be able to shoot your dad's Grizz well, but it will draw about 55 pounds for you, and it is not the bow for you to learn on. - lbg