Yes, literally everyone will eventually die of old age. You're such an enlightened genius for figuring this out, anon. But if you die of old age AT A LATER AGE THAN YOU OTHERWISE WOULD HAVE then you have, by definition, EXTENDED your LIFE. The goal of this type of research is to figure out how to radically extend human life expectancy well beyond what we currently consider normal. It's done in bits and pieces, a couple years here, a few more years there, honing in on the exact mechanisms and how to slow, halt, or reverse them. What I hear you say is, "You'll die eventually no matter what so it's all bullshit.">If you just want to be healthier and die of old age, you can have a good diet and exercise frequently.
But is it not worth figuring out WHY that is the case? Figuring out WHAT constitutes a good diet? If and how we can distill those effects into some other delivery method or even simply amplify/enhance those natural effects to make your diet and exercise go even further in improving your health and slowing your aging?
You seem to think we have it all figured out, but even something as seemingly simple as "diet and exercise" is very complex and controversial.