May 2, 20xx
( 时间写在右上角)
Dear Lucy，
Next Monday is my 20th birthday. Imagine, there are already twenty years behind me! No wonder I feel old!
My parents are giving a dinner party to mark the party. The first person they wish to invite is you, my childhood pal. Indeed, all of those 20 years are more or less associated with you.
We'll be expecting you any time after six. See you then.
Yours,
( 落款写在右下角，标点是逗号)