My FIL also talks the sameway as your FIL.
Initially I used to feel too bad and even grabbed the opportunity to go out of India cos of ILs. But then now after relocating back to India, he hasnt changed but I'm ready to be with them just having their age factor on my mind. Even now he passes such comments but I totally ignore it.
IMO In-Laws are not GOD.And conduct certficate from them is not going fetch us a place in heaven. So I dont try please them at the sametime I see to it I dont hurt them either.
Even if they pass coments are anything try to ignore and be yourself. We need to be true to our conscience only.
If you try to please everyone in the family n try to get into their good books, then at the end of the day you will be depressed and will feel like a doormat. bcos no one is going to appreciate you or even acknowledge ur good deeds.
My formula of staying at peace, I dont hurt others and I dont allow others to hurt me. Atleast I dont show that I am hurt. Their only aim is to provoke us. But when you become resistant to their comments, they might stop commenting someday

. Before that you might get used to their comments. One thing for sure you cannot change them. They are like that.Learn to survive with them.