GURPS Aging Calculator

My apologies, dear reader. Today is not GURPS-Day — but I am blogging about GURPS, because on GURPS-Day this week I felt rather shitty. Still do, in fact, but today I felt well enough to make the first post of the new year in my ongoing GURPS cyberpunk game, Hello World.

Many moons ago, back in the dark ages of 2007, I wanted to do some visualisation of the GURPS aging rules. So I put together a Perl script that did a couple thousand die rolls and did some math on them. Over the years I added to and refined this script — in 2014 I made it multi-threaded, speeding it up by quite a factor. Earlier this month I rewrote it in Rust and made it a lot faster — and also made it easy to maintain a Windows version, so those of you that want to play along at home don’t have to install Perl to do so. You can find it on Github.

For the most part, I’ve just used it to tell me what age a character is likely to live to. But tonight, I was doing some setting work for Altered States — the world that Hello World takes place in (more about that setting next GURPS-Day). For this setting, I stole a page from Transhuman Space — almost literally. Transhuman Space: Fifth Wave has a page with a comparison between the Statistical Abstract of the United States, 1990 (real-world) and 2090 (game world) editions.

I did one for my own setting, between the 2010 and 2065 editions. This précis lists, for my world, a life expectancy of 106 years. Now, this number was mostly pulled out of thin air for setting design reasons — I have nothing to support it. So let’s see what rules I do need to support it, hmm?

The four relevant options for my aging calculator are --death, the HT a person is considered dead upon reaching; --ht, the average HT of the population in question; --tl, the medical TL of the population in question; and --add, any additional modifiers to the aging roll. My calculator assumes a default death at HT 4 — even with advanced medical science, you’re not going to have much life left after this much aging. Average HT is of course 10. The setting is verging on TL10, but medical TL is dependent on the TL of most of your lifetime medical attention, so we’ll go with TL9. And for now, let’s avoid any additional modifiers to the roll.

celti@siduri ~ $ gurps-aging-calculator --death 4 --ht 10 --tl 9 --add 0
Median age of death is 90 (highest is 231.25, lowest is 53).
Mean is 90.52565; StdDev is 16.73338245509202.

No, no, no! This won’t do at all! According to GURPS, most people won’t live past 90. We need at least another twelve years for me to be happy. So… let’s assume standard medical treatment, when a fellow gets old, includes a regimen of anagathic drugs — maybe the pending trials on metformin will pan out. That’s quite clearly a modifier to the aging roll, so let’s call it… +2.

celti@siduri ~ $ gurps-aging-calculator --death 4 --ht 10 --tl 9 --add 2
Median age of death is 101.5 (highest is 295, lowest is 53).
Mean is 104.78382; StdDev is 20.51474606242245.

Oh, so close. Just half a year off from my “good enough” target. Maybe a +3 will do the trick?

celti@siduri ~ $ gurps-aging-calculator --death 4 --ht 10 --tl 9 --add 3
Median age of death is 104.75 (highest is 279, lowest is 53).
Mean is 108.046465; StdDev is 20.715791770870293.

Bingo! But now I wonder, how close to exactly 106 years old can we get? Another +1 gives us…

celti@siduri ~ $ gurps-aging-calculator --death 4 --ht 10 --tl 9 --add 4
Median age of death is 111 (highest is 312.25, lowest is 53).
Mean is 114.9135025; StdDev is 23.828153891283254.

Nope, way too high. Instead… maybe the wonders of medical science will let us live even at HT 4? Let’s bump death down to HT 3.

celti@siduri ~ $ gurps-aging-calculator --death 3 --ht 10 --tl 9 --add 3
Median age of death is 106.25 (highest is 292, lowest is 53).
Mean is 109.70786; StdDev is 20.53517098547977.

Bingo! I don’t think we’ll get any closer than that!

Bonus Credit: Transhuman Space

Just for fun, let’s play with the same figures for Transhuman Space. They give a life expectancy of 138.5 years, and are TL10 verging on TL11. Now, they play havoc with the aging rules, changing thresholds, making them versus HT+5 and modified by Wealth level, but let’s try and fit them to the normal aging rules.

celti@siduri ~ $ gurps-aging-calculator --death 3 --ht 10 --tl 10 --add 0
Median age of death is 94.5 (highest is 232.5, lowest is 54).
Mean is 96.3838625; StdDev is 16.50542557000078.

That puts them forty-four years below the stated average. Unfortunately, with the way the aging rules work, there’s a cap on just how much additional modifiers will help, and for our current parameters that cap is +5.

celti@siduri ~ $ gurps-aging-calculator --death 3 --ht 10 --tl 10 --add 5
Median age of death is 124.5 (highest is 328, lowest is 55).
Mean is 128.728195; StdDev is 26.873046438731865.

Still puts us fourteen years too early, so it looks like we do need some modification of the aging rules. The big one Transhuman Space uses is they increase the ages at which aging start, and speed up, by twenty years across the board. That means we need a target age of 118.5. Let’s put death at HT 2 — that’s the point where you cannot possibly pass an HT roll without medical aid — and give a bonus of +4.

celti@siduri ~ $ gurps-aging-calculator --death 2 --ht 10 --tl 10 --add 4
Median age of death is 118.25 (highest is 324.5, lowest is 59).
Mean is 122.224785; StdDev is 24.13707824984686.

And there you have it, folks.