You can start teaching your kids after 14 or 16 months. But you can't just expose your child to reading on that stage. First try to teach him words pronunciation and identifications. There are many teaching apps are also available for your kids learning on iPhones, and computers online.
I'm using a wonderful reading program called Children Learning Reading by Jim Yang. My son can now read level 2 phonics book independently. Check out his learning milestones from my blog.
No matter what your child's age, you can start exposing them to reading by reading to them. If they still cannot understand the words, the sounds will stimulate them and help them learn listening skills. If they can understand the words, it will help grow their vocabulary. Plus, reading together is a great way to bond with your child while helping them learn the meaning behind specific stories.