Birthday milestones are significant ages that often hold special meaning in various cultures. Common milestones include turning 1, 5, 10, 13, 16, 18, 21, and 50. Each of these ages can represent a transition, such as moving from childhood to adolescence or reaching adulthood. Celebrating these milestones often involves unique traditions or parties. For example, a 16th birthday is commonly celebrated with a quinceañera in some cultures, while the 21st birthday is often marked by a celebration of legal adulthood in many places. These events help individuals reflect on their growth and achievements.