My stepson is 21yrs old, we just traveled all around Thailand
I asked him if he's tired about the masks and will he wear it when he doesn't have to.
He said he is tried and will ditch the mask once he can(which he can now) but then likely didn't give it another thought
I was surprised how quick my wife ditched the mask once back in Canada, I thought she'd be a permanent mask wearer
On entry with a Non Imm O-A Visa, you'll be granted temporary permission of stay up to 1 year, subject to the expiry date of your Health Insurance. (Have your Insurance start date dated the same day you intend to enter Thailand).
They can then extend their permission of stay to match yours.
This is detailed in section 2.20 of Immigration Bureau Order 327-2557 (2014) - Criteria for extension ENG.pdf