To write a retirement greeting, first consider how well you know the recipient and what kind of relationship you have had with them. If it is a co-worker or a boss, say something like, "It has been an honor to work side-by-side with you for so many years. Congratulations!"
If the person retiring is a family member or a friend, the message can be more personal. For example, if the recipient is your husband or wife, say something like, "I am looking forward to our many adventures now that you are retiring! Here's to us and our new horizon!" If you are the daughter or grandchild of the retiree, a similar message is, "I'm so happy that you have reached this milestone. I can't wait to spend more time with you, support you the way you have always supported me, and watch your new journey unfold."
Write a funny message if you know the recipient well and have a good rapport with him. Remember to be gracious and light-hearted, never mean or dark. Write a joke like, "Good luck with your new boss! Remember, happy wife, happy life." When the recipient is a colleague, it is good to mention how invaluable the person's work has been to the company or to the field in which they specialized.