From the webpage of the Thai Embassy in Warsaw, the one you like to use to apply:
The Royal Thai Embassy cannot accommodate urgent requests. The applicants must ensure that they leave sufficient time for their visa application process before their planned departure.
So your husband of wife in a unmarried marriage having a real estate agency.
You are going to sell/lease/rent real estate somewhere in the world BUT NOT in Thailand and you are going to that on-line, You as agent show the property, discuss with clients, sign contracts and hand over the keys using a key board and the www.
Yep I need to figure out how that is going to work, specially having a spouse but being single.
Every foreigner visiting Thailand need a legal stay which they get based on passport at immigration checkpoint.
This could be the short time tourist entries, like Visa on Arrival, Visa Exempt Entry, Tourist Visa or the long term visa, like Non Immigrant or DTV.
There is NO minimum age or even maximum age.
The story that some parents love to hear, is that by Thai law, children (Thai and foreign) can not get a fine until the age of 15 years, that is why you see children doing exercise after being stopped at traffic stops. NO FINE but exercise.
Some people advice you to ignore the law as no fine means you are allowed to break the law, your insurance company sees it different and same as schools.