//what is a good way to discuss about these matters with my parents?//
Patiently
I think it's safe to assume that as you get older, in certain people, their patience threshold tends to diminish over the said years.....internet loading slowly, cooking takes too much time to cook it and only 5 minutes to eat it etc....they are your parents and, as you say, very happy with how they raised you....everybody complains about something, no matter what age they are so, to quote our resident AB quack, Sqad.... no big deal, monitor the situation and see what happens.
I'd like to sort of complain that my wife of 25 years is currently in the kitchen making a cake, 'singing' ( and I use the term very loosely) along to Rita Ora's 'Anywhere' amongst other tunes... ......do I complain?....nope, as long as she's happy, I am too......now, where are those ear muffs :-)