The answer on your question is not to easy to give because there are lots of
options here.If you own a property and do not have a work permit you are in fact allowed to
stay for only 90 days on a visitor’s entry stamp at the immigration check point
on arrival. There will never be any serious problems for you to stay 90 days.
If you do want to stay longer than these 90 days, then you better apply for a
visa from abroad before entering the Kingdom. This will ensure that you can maximize your stay within any given 12 month period and extend it constantly. If you are at the age of retirement in this paradise. you can get a – a non-immigrant ‘O’ visa, also obligated to obtain outside Thailand. If you are already inside Thailand you will have to go outside to a Thai embassy in another country. General Requirements are that you suppose to be 50 years of age or older, in a good health with a police clearance from your home country or embassy telling the Thai authorities that you ‘behaved’ in your country. But most of the authorities not even check that. The same retirement visa will be granted if you have deposited a minimum of 800,000 Thai baht in a Thai bank with proof that this money came from outside Thailand or you have a monthly income from your country of minimum 62,000.00 THB. Mostly a pension is enough. Another option is a VIP visa that cost you 1 million Thai baht and gives you special rights such as no 3 monthly visa runts, all aimed at to make your stay in Thailand very comfortable, as a real VIP is suited. If you come to work in Thailand and apply for a work permit and will get a 1 year visa without any problem. And no matter what age you are, it is always possible to get a student visa what every visa office or recognized language school in Thailand can provide you at different prices but the 1 years stay is ensured. You also will get a 1 year visa after you fulfill the requirements that the kingdom has set up.
The final answer to your question of how long you can stay in Thailand is in fact ‘ As long as you want, you can stay in paradise Thailand….