It even says so:

"Retirement End Year - Time to get real grim here… this is when you’re expecting to not need your retirement fund anymore. Put in a different way, it is when you expect to die. There are a number of factors that play into this, but I would suggest looking at the Social Security Administrations chart here. As of the date that I wrote this post, I am a 39 year old female, and that chart tells me that on average I can expect to live 43.41 more years. So, I personally would set the Retirement End Year to 2072 (2021 + 43.41 = 2062.41 + 10 years of padding just to be sure)." -- https://www.cfiresim.com/tutorials/