I filled up most of my sketchbook with drawings of my Mom. I don't get tired of doing them because I try to make each one better than the last. Each time I draw her represents another chance to go at it again and get it right. I don't see myself getting tired of drawing her when There is so much to get right. It's always about making a better drawing.
Maybe I need to try to do a bit more, introduce some color or try to get more of the room she is in. But there is so much to get out of drawing her head. The expressions on her face, her hair, learning to simplify the drawing. Choosing only the lines and marks that can give the image meaning. Its not just about the subject but also how you communicate visually what and how you see. That way the drawing becomes more of an experience if I can just communicate those things I mentioned in the drawing.
Pursuing those things can take up many sketchbooks and never get old.