When did you first introduce colouring books to your toddlers?

Whenever toddler shows the interest in using the crayons I would say they are ready. My nephew is almost 23 months and just loves coloring. I think I introduced them at around 16 months. I've even let hem use felt pens, dot dabbers, and paint (I've sat with him when he has used these). He also loves sticking stickers to all her works of art.