You get a 60 day visa exemption on arrival. Just make sure you meet the requirements for adequate funds and have lodging. The airline will also require proof that you have a return ticket or onward travel tickets.
my wife (Thai) does my marriage visa for me. The initial application process is somewhat daunting. There's a lot to do. It gets easier after the first time. In my case, I went to the Thai embassy in Chicago. They gave me a 6 month, multiple entry tourist visa for $200.00. Not sure what's available nowadays. A retirement visa can be easier to do, but requires more money in a Thai bank account plus health insurance. At his age, insurance might be very expensive or difficult to get. I'm not sure about that since it's not a requirement for marriage visa.