What's new is people typically living beyond 70, and the myriad of failure modes that exposes. Many illnesses such as dementia will completely consume the lives of multiple caregivers.
People have been living over 70 for a long time now. Statistics was skewed because of higher child mortality in deaths at birth.
Maybe, but the percent of US population that is 80+ has grown quite a bit. For example, between 1950 and 2020 the percent of those 80-84 more than doubled. In the same period those 85+ went up five-fold (source: https://www.urban.org/sites/default/files/2015/10/09/t2_age_...). IMO this is the result of modern medicine extending lives well beyond where they would have gone before. Based on my parent’s experience, once you’re kept alive by machines and medicine, your quality of life sucks.
The percentage in the population went up, because there are fewer young people (their percentage went proportionately down with a huge drop in the under 18 category). I'm not claiming the modern medicine doesn't help, but it's not evident from your linked table.