Answer:
Dear...
Please accept my congratulation on your eighteenth birthday that falls on this day. I wish you a very long life, and pray to God for your prosperity and happiness.
I hope, on the occasion of your birthday, you will invite your friends who are near at hand, and cut your birthday cake in their presence.
On the occasion of your birthday, you must have been presented with new clothes and other precious gifts by your parents- and friends.
Please write to me at your convenience.