Hey, so, did some (extensive) math on your Youthful gene, and I think it's currently tuned too strong.

Currently, as written, a pawn would take 68.4 years to go from 18 to 35 (versus 17 normally, so 4.02x as long), 13.7 to go from 35 to 45, 4.05 from 45-50, and 4.6 from 50-60. Net is taking 22.35 years to go from 35-60, versus 25 without the gene. Not much of a penalty there. Going from 18 to 80 (defined "average lifespan" for humans in the game) takes 108.8 years, versus 62 normally. In fact, a pawn with this gene spends more time between 18 and 35 than a normal pawn spends alive after 18 (on average, and assuming death from old age). I believe most Rimworld games are not going to last nearly long enough for a pawn with this gene, as it currently stands, to start seeing any form of age-related issues (which *mostly* start showing up after age 45-50, taking some 82 years to reach with this gene currently).

I did some poking at the aging curve, and this is what I came up with as a suggested alternative:


This results in a total of 59.945 years from 18 to 60, versus 42 normally, and then 66.611 years from 18-80, versus 62 normally. The pawn spends 73.5% of their adult life (18-80) between 18 and 40, versus 35.5% of it normally. The pawn spends 42.3% of their adult life between 18 and 25, versus 11.3% normally.

So it's still a very significant boon (honestly, should probably cost more than -1 Met, since the base game alternative, Ageless, costs an Archite Capsule), but less of a lifespan-extending gene and more of a "spends more time young" gene. It just shifts what percentage of the pawn's life is spent young and hale, versus old and infirm, without significantly adjusting their average lifespan.

Addendum: here's a link[www.wolframalpha.com] to a Wolfram Alpha set up to solve for the time a pawn spends between two ages, given curve points like above. `A` is the lower age limit, `B` is the upper, `a` is the aging multiplier at age `A`, and `b` is the multiplier at age `B`. It'll throw a fit about the computation taking too long, but that's just for the other solutioning it does, it'll still spit out the numerical answer (in years).