Do I need a re-entry permit to travel out of Thailand with a retirement visa?

Yes get a re-entry permit either from your local immigration office, or at the airport when you are leaving, assuming you do not have a multi entry.

Unless you're on a multiple entry visa, get a re-entry permit.

@Jeff *******

If you still have a visa, you’ll need to check if it’s a multiple entries visa as Graham already mentioned. A regular 90 days Non O visa is rarely issued as a multiple at date. If you leave you’ll probably need a re-entry permit. A Non O-A one year visa is always multiple.

If you’re already on your first year Extension of Stay, you’ll need to by a re-entry permit. They’re sold as single or multiple re-entry permits at your local immigration or at the airport short time after you pass through immigration.

Yes, get a re-entry permit if your Visa is not multi-entry or you lose your status when you stamp out