For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
What is "long life?" Who gets to define what it means to have a long life? The meaning depends on who you ask. The answer depends on the era in question. What was considered a long life when the fifth commandment was given? And then 1400 years later when Jesus was on earth, how many years did you need to live to be considered to have lived long?
God doesn't give us a moving target to try to hit, and long life is definitely a moving target. Medical breakthroughs are the major reason that life expectancy has been extended so much. Of course, these breakthroughs are God-given; were they given because the inhabitants of the earth honored our parents? That's debatable.
Mr Kraft's comment in the answer section is indicative of what the fith commandment was all about. He says his elderly parents got in a pinch and he and his immediate family took them in and cared for them until they rebounded. That's exactly what God was /is telling us to do. 'Don't devalue the lives of your parents by leaving them to fend for themselves, and the life of the nation will be lengthened.'
Then Mr Kraft told us more: he says he lost a son at 42 years old and he had a couple of grandchildren die very prematurely. His examples are eye-openers.
We can't purchase anything from God by our actions. He gives us principles to live by that will honor both him and us. And he makes his sun rise on the good, and sends rain on the just and the unjust (Matt 5:45). God doesn't make deals, he makes promises!