Actually, the average lifespan at 65, i.e. how long can you expect to live given that you've reached 65, has seen a much less dramatic change than life expectancy at birth (often called just "life expectancy"). In 1845 it was 75 years, today it's 82 (data for the UK [1]). Since people who die before 65 don't get any retirement, this is the key figure.
Looking at the graph in that source, life expectancy at 65 has been increasing roughly linearly since ~1900, with a trend around 0.7 years per decade. This means that kids entering the workforce today who survive to 65 can expect to live about four years longer than people entering retirement today.
Given that retirement age is now steadily increasing, it's not likely that people will have significantly longer retirements even in 2050. Four years of increase in retirement age from now until 2050 is highly likely IMO.
Edit: forgot source link:
But IMO this is very unlikely, because people die of such wildly varying causes (including lifestyle-induced diseases, accidents and even suicide) that it's hard to imagine what this sudden change could be.
More likely we will keep seeing incremental change, disease by disease, steadily increasing average lifetimes.
Biology and biochemistry is so bloody hard compared to any human tech, it's amazing we have come as far as we have today. People talk about curing cancer like going to the moon, just throw money at it, but that analogy is only accurate if you assume starting your space program sometime around 1870.
Past performance is no guarantee of future results.
Past results guarantee future results in the same circumstances. Over time, circumstances change which invalidates their value. But, in the short term, they imply a probability of future results based off of the volatility of the circumstance state.
Not comforting at all.
1. Technology innovation velocity will increase, with the results distributed through society, driving down the cost of living (this is already happening with almost everything except real estate, healthcare, and education [1]). You won't need to invest, because it'll cost nothing to exist (let's call this "Star Trek Future").
2. Technology innovation velocity will increase, but it'll be locked up with copyright, patents, etc. Rent seeking will drive more of the population into serfdom. You will not have a pleasant life, nor will it be long (we'll call this "Elysium Future").
[1] https://www.washingtonpost.com/news/wonk/wp/2016/08/17/the-s...
2. See #1. Diversification is the way to reduce the risk of stock market crashes, while still getting high annual returns. Diversied portfolios such as the Permanent Portfolio have averaged 9.3% CAGR over the last 40+ years.
3. Average lifespan in developed countries is still increasing dramatically. It might be ~80 years now, but kids just entering the workforce could easily live 100+ years. You better plan for it, unless you want to work right up until the day you die.
4. Agreed.