How many years is milestone in ages?

A milestone typically refers to a significant event or turning point in a person's life, and it can vary in meaning depending on context. In terms of ages, milestones often include birthdays such as turning 1, 10, 16, 18, 21, 30, 40, and so on, with each age representing a new phase of life or legal status. Therefore, the concept of a "milestone" can span various ages, but it generally refers to specific years that mark important transitions rather than a fixed number of years.