After retirement I will get a monthly pension from my Thai employer, (around 42,000 Baht).

Do I have to pay income taxes for this amount or not?

If yes, how much I can deduct after age 65.

WCA

Someone else will have to answer with regard to Thai taxes. I don't think the pension would be taxable but I am not an authority on Thai taxes.

If you are an American, the pension will be taxable in the U.S. If that is all the income you have, you may not owe much, in anything, because of the standard deduction and personal exemption. Just be aware that the Foreign Earned Income Exclusion, currently up to $82,500, does not apply. Only payments for current services, either in the year for which a return is filed or for the immediately preceding year, qualifies. Pension payments don't meet this requirement.

I am not an American and this pension as well as another one from abroad will be tax free in my home country as long as I live abroad

WCA