Will airlines require a return ticket for a retirement visa applicant flying from the US?

Correct, but I felt the OP did not know about how the O-A visa actually works - and I was correct - and another fellow picked up on a useful aspect of the discussion. The correct info was given directly related to the actual question - at least two times - one by me. From his remarks the OP was quite pleased with all that he learned.

The original subject was about airlines and nothing to do with visas

Yes, David and this is not the subject of O-A visa discussion

The original subject pertained to the Second Year of an O-A visa (having nothing to do with an Extension of Stay)

David, not sure but you may be crossing the two Visas / Extensions... An Extension of Stay done each year on an O Visa is not the same as much of this discussion relating to an O-A visa. Extensions of Stay done for one year always has the option of buying Reentry Permits should you want to Exit and Return to Thailand.

You'll need to get a reentry permit every time you leave. The reason they want you to retire here is to get your money.. You will always have to pay.

Thanks, I learned something new here too!

Absolutely , and exactly what I did with my first one , I got 23 months and 2 days on mine before I had to do my first extension.

Just watch your "Enter before" date on your O-A visa, not the date you stamp in the first time. For example, my O-A, issued at the Thai Embassy in DC on 6 November 2015, had an "Enter before" date of 5 November 2016. I first stamped into the Kingdom on 15 November 2015. Upon entering I had permission to stay in the Kingdom for a full year (until 14 November 2016), but I had to leave and reenter *before 5 November 2016* to get stamped in for that second year. If I had missed that date I still could have applied for an extension, but it's easier just to take a quick, cheap flight to Kuala Lumpur, even if only for a day.

The only caveat to this is that your second year does not extend your multi reentry permission granted on your original visa. The second year you'll need to buy your reentry permit(s) or your stay is no longer valid from the moment you stamp out.