Or something else I am not thinking of?

If it's a cake order I would just call the person that placed the order and ask them what they want written on the cake.

If you're doing it for some one you know and it's not an order I've had people request- "Congratulations and Best Wishes on your retirement",
"Good luck from all of us on your retirement", "Wishing you a fantastic retirement",

HTH

The last ones that I did was for a group of three men and they had wanted "Happy Retirement ____" then below that on a slant I wrote "Thank you for all of your years!" They loved it. Just another thought for ya!

I did a retirement cake for my sons teacher, it read....

Congratulations Mrs. ____

We will miss you!

You could use this if it is a large company, or from a group of people.