If you are on a laptop then sometimes there is a function key that converts your JKL key area to a nueric keypad. then your nudge up down left right keys will work as page up and page down keys.
Otherwise there is the next frame and previous frame buttons on the Preview Panel.
AE does not have a keyboard shortcut editor like Photoshop does. Afraid you are out of luck there.
Ctl/Cmd-cursor right & left also work on most machines. Add the shift key and the cursor goes backwards/forwards by 10 frames.