Can I travel to Laos with a retirement visa in Thailand?

If you mean you want to travel to Laos and back, yes, you can. Thai visa-wise, you need to get a re-entry permit before you leave for Laos to keep your current stamp alive. Then you will be able to enter Thailand again on your current retirement visa entry (or extension) stamp. But you need to be back in Thailand within your current stamp valid. A re-entry permit wouldn't add any day to your current stamp.

A re-entry permit is available at your local immigration office or the office that issued your extension in case you are on an extension, OR international airports on your departure.

attached is general information for re-entry permit.

BTW, the entry requirement to Laos is out of the scope of this group. Ask Mr. Google or recent ai-s are your friend about that.