How old do you have to be to wear sunglasses?

The best protection for a baby from sun is a hat with a brim and the appropriate use of sun screen. There is no reason why a child under one year can't wear sunglasses, as long as they are rated to meet safety standard ANSI Z80.3. This standard specifies that the glasses meet the proper safety level for this type of eyewear and use and includes UV protection and impact protection. Most high-quality sunglasses will conform to this, however, cheap spectacles that you may find in a novelty store or other retailer who is not a professional eyewear dispenser may not. Check with your licensed optician.