Milestone birthdays are significant ages that often hold special meaning in various cultures. Common milestone birthdays include turning 18, 21, 30, 40, 50, and 60. These ages are often celebrated with parties or ceremonies, marking important transitions in life, such as reaching adulthood or entering a new decade. Celebrating milestone birthdays can involve traditions, such as throwing a big party, giving special gifts, or reflecting on personal achievements. Many people use these occasions to gather with family and friends, creating lasting memories and acknowledging the journey of life thus far.