大寿 specifically marks decade birthdays of elders, typically from age 50 onward (
六十大寿,
七十大寿,
八十大寿). Celebrating an elder's
大寿 is a major family event with banquets, longevity peaches (
寿桃 shòutáo), and
寿面 (shòumiàn longevity noodles). Calling a young person's birthday
大寿 would sound joking or sarcastic.
