Dear (your name),
Hey, how are you now? I am (your name) five years ago.
I don't know whether you have reached your goal or not but I hope you will always remember how hard-working you were when five years ago.
Work hard makes everything success. Therefore, you should keep hard-working to your next goal and keep finding your next goal so that you will have your power to fighting.
Also, don't be so sad to hardship. Hardship is the best training for yourself. It helps you to become more tough and makes you become more mature.
Yours,
(your name)