When a person who has an O-A visa and finishes the two years that person has an option of Applying for an one year Extension of Stay based on being age 50 or over.. Or they can go back to their home country to get a new Non Immigrant O-A Visa.
He can do it again - Exit and Renter several more times - if he wants to... right up until a day before expiry... If he just wants to travel or whatever. No Reentry Permit needed with the O-A in the First Year - it is a Multi-Entry Visa 'M' .
This post depicts the great benefits of the Non Imm. O-A Visa. ... basically 2 for 1.
Exiting and Reentering Thailand near the First year expiry date (enter before / valid until) assures another near full year of use. A really good deal!