The biggest birthday tradition in Korea is probably drinking miyukguk, the seaweed soup. My host mom always serves the soup for breakfast whenever it is a family member's birthday. In Korea, it is common for people to ask if you've eaten miyukguk on your birthday.
Age and respect are very important in Korea-. Students in the same grade are always in the same age group. For instance, all of my fifth graders have a Korean age of 11. If you meet someone even a year or two older than you in Korea, it is customary to refer to them as "older brother" or "older sister" instead of just saying their name. Having everyone change ages at the same time keeps different age groups distinctive. At the same time, individual birthdays are still really important. Everyone appreciates the time to gather with family and friends and enjoy their favorite foods and activities.
The biggest Korean birthday tradition, eating miyukguk, is definitely connected to Korea's environment. A lot of Korea is near the water, so seafood and seaweed play an important (and delicious) role in many Korean dishes. Kim, seaweed, and kimbap, seaweed rice rolls, are two of my favorite snacks. Miyukguk is a similar seaweed-based dish that tastes really wholesome and delicious. Seaweed is rich in iodine and calcium, so many new mothers drink a lot of miyukguk to be healthy and keep their babies healthy, too.
