Allow me to congratulate you with all my best wishes upon your having reached your 年龄 birthday. May you live a long, healthy and joyful life.
在您___大寿之际，请允许我向你表示最衷心的祝福，祝你健康、长寿、生活愉快！
下面这个也不错：I know I keep you busy ,but you keep me busy,too.While you"re busy taking care of me ,I"m busy loving you .Have a wonderful birthday!
希望你能满意！