90th birthday
Refers to the celebration of one's 90th birthday, derived from the character 卒 which can be read as そつ and decomposed into 九十 (ninety).
My grandfather will celebrate his 90th birthday next month.
卒寿のお祝いに家族が集まった。
The family gathered to celebrate his 90th birthday.
Refers to the 99th birthday celebration, derived from the character 白 which is 百 (one hundred) minus one.
Standard kanji spelling for the 90th birthday celebration.
Alternate kanji form using the variant character 卆 for 卒; rarely used.
From the decomposition of the kanji 卒 into 九 (nine) and 十 (ten), representing ninety.