Thanks for sharing your thoughts.
Regarding your life expectancy when you reach your 60s, it's actually likely to be much higher than you think based on e.g. the SSA's actuarial table (https://www.ssa.gov/oact/STATS/table4c6.html), which for American men at 62 is 20.27 years (so until age 82.27).
You can get the full details here: https://medium.com/crows-feet/how-to-have-your-best-retirement-feel-confident-and-never-run-out-of-money-33af3a5f5385, but if you're well-off, you might expect to live up to an extra 13 years relative to the average.
That puts your average expected age at death around 95. And if you consider that you have a 50% likelihood of living longer, sticking around past age 100 isn't ridiculous to plan for. After all, according to the SSA, you have a 25 percent chance for an extra five years and a 10 percent chance of an extra 10 years!
Sure, as you age you tend to spend less. Statistically, it's around 1% less each year you age. As for SS benefits, in about 12 years, the trust fund will be exhausted, and if Congress doesn't do something different, benefits will have to be cut by 23% (https://www.cnbc.com/select/will-social-security-run-out-heres-what-you-need-to-know/).
According to the SSA, "In 2019, the average annual Social Security income received by women 65 years and older was $13,505 compared to $17,374 for men." (https://www.ssa.gov/news/press/factsheets/women-alt.pdf).
Adjust upward by the COLA increases for 2020, 2021, 2022, and 2023 and take off 23%, and you have $12,320/year for women and $15,850/year for men. This compares to the official Us poverty line of $13,590 (https://aspe.hhs.gov/topics/poverty-economic-mobility/poverty-guidelines).
That means a woman would be 9.4% below the poverty line, while a man would be 16.6% above it. Either way, I don't see living on $1321/month, let alone $1027/month, in the US as anything more than abject poverty.
As for the risk of living too frugally, exactly! That's the second benefit of the guardrail approach (see more here: https://medium.com/crows-feet/your-single-best-way-to-avoid-running-out-of-money-in-retirement-a9793e0eb5cd) - you can spend on average more than 25% higher amounts compared to the 4% rule, with far lower risk of running out.
