What requirements must a 71-year-old retiree meet to extend their NON-O visa in Thailand after 21 years?

A 71-year-old expatriate in Thailand, holding a NON-O visa based on retirement, seeks to understand the requirements to extend his visa for an additional year. He has been living in Thailand for 21 years and heard that if someone has been in the country for over 20 years, they might only need to show a bank balance of 220,000 Baht or a monthly income of 20,000 Baht. However, local immigration officials were uncertain about this guideline. Some commenters mentioned the existence of a 'grandfather clause' for those with uninterrupted extensions since October 21, 1998, which may allow for reduced financial requirements. It's recommended that the individual verify his extension history and gather necessary documentation, as requirements can vary and some officials may not be aware of these nuances.