May 2， 20xx
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.
Well be expecting you any time after six. See you then.
Yours，