I would classify those mentioned above as "novelty fabrics" and as far as I am concerned there is no age limit where they should or should not be used.
I did a quilt for hubs and used many novelty fabrics to represent his interests such as trains, cars, cheese, wine, letters of the alphabet to represent his profession as a teacher, books, trees, basketballs etc.
I often find that it is the way things are said that can be very off putting.
I look forward to seeing the quilt that you end up making.