Yes no limit (air), but always remember it is ALWAYS up to the Immigration official. So if they decide that you have 'Too many' in their eyes, they may give you a warning. Always carry 20k baht in cash to support your stay, should they ask (as this is a requirement whether they ask or not). I would also recommend choosing male IO's at the airport and not female as they like to make a scene a lot more than the men. (again not sexist, factual).
You have a visa exemption, not a tourist visa (this is 60 days). Also you are not doing visa runs, you are doing border runs by land or leaving and entering by air.....There is no limit by air....only by land......why not go and get a visa from Laos or another consulate....? and extend for 30.....= 90 day stay.......There are various agencies that can take you there.....or get a cheap flight to Udon and cross the border by bus.....
You have a multiple entry visa. You can enter for 60, extend for 30, then leave and come back for 60 and extend that for 30 again. If you re-enter before the 'use by date', you can get more time from your visa.
David I am just refering to terms used. That he will be extending a NON immigrant O for a year based on retirement. He can't have his O visa "extended (within Thailand) to an ‘OA’ retirement upon your 50th". OA can only be obtained outside of Thailand.
David an OA visa can only be applied for in your home country. You also need the money in an account in your home country. As he is not 50, he is not eligible for this. So as you mentioned he needs a NON imm O before 50 which can be extended for a year (not to an OA) based on retirement where the money is in a Thai account or income statement.