It is well known that there are vast differences in the ages at which children can do something for the first time. The first time they ‘walk’ is one example of that. Keep in mind that every child develops in their own way.
Some children ‘spontaneously’ start walking around eight months. That is straight after the brain is first able to understand what walking is. Another child will have little interest in walking. They do other things first, things they find more important. And that child may postpone walking until they are two years old. That is also quite normal. Most children, however, take their first steps around 14-15 months. On average, girls take their first step a month earlier than boys.
Every child chooses to start walking when it suits them. Therefore, you cannot compare what one child can or cannot do with what other children can or cannot do. And that is why such a new skill can never be age related. This also applies to ‘the first word’, ‘the first tower of blocks’ and so on. Every child develops in their own way!