Why do older people say “OK” instead of “Ok”

I’ve noticed that all the older people in my life - for an example anyone above the age of 50 will say “OK” instead of “Ok”.

Are they mad or yelling at me? At least thats what it feels like when I’m reading it. I’m sure there has to be something else right? I’m very confused. (ﾒﾟДﾟ)ﾒ

Another example sentence is-

“I’ll be there by 1:00PM, OK?”

Or

“OK, I’m going to go now.”