Another similarity is that children are ready for the process at different ages.
While most babies start getting teeth when they're around six months old, once in a while a baby is born with some teeth already showing and others don't get their first teeth until after their first birthdays.
Reading readiness also happens at different ages depending on when the myelin coating on nerves in the brain finishes growing. Usually kids are ready to read when they're about six years old, but some are ready in preschool while others may not be until they're around eight years old. Becoming ready to read at an earlier or later age doesn't necessarily show intelligence levels any more than the age of getting teeth does.
However children who are expected to learn to read before they are physically ready to do so my learn to fail. If they become convinced that reading is something they are not capable of doing, they may give up. And if, when they do become ready, they're expected to use material designed for kids who are already fluent readers, they won't be able to do it.
That's why I believe children who are developmentally ready should be allowed to learn reading in Preschool and Kindergarten, but that should not be a requirement. If a child doesn't learn to read in First Grade there should be no stigma attached to repeating that grade.
And parents certainly don't need to be ashamed if their babies don't get their first teeth as early as others do.