Is Aging a preventable or curable disease? or is it natural?

Aging is an engineering problem, so yes soon enough when the technology allows we can start to tweak it. At the moment we're staying alive mostly because of finding ways to stave off the things that kill us, but leaving the aging process untouched. The 'three score and ten and four score if you're strong' notion still holds true. The greatest impact we've had on overall longevity isn't at the end of life, but at the start.

In the late 19th century nigh on half of all people died before the age of five. That really skews the stats. There have always been old people, but before now there were also many graves of the very young.

I recall a thread here on AH where we were asked if medical science saved your life and there was a huge number of people who wouldn't have made it to 20 without medical intervention. Getting the same folks to 100 requires more than intervention and prevention, it requires really low level engineering.

Still, yep I reckon we're unlucky in one way in that while quite the number reading this will see 100, we're likely about 50-100 years away before a time when living to a thousand is near a given and death one chooses is mostly down to boredom. That's going to fundamentally change the way we see ourselves as human.