It seems to me they don't die of old age. I am in year 93 now, and from year ±20/30 no kittens died I think. My first kitten still has an age of 16, and I know for sure I have her for longer than 16 years. (Her skill level is proficient 20%, and I was keeping track of her skill increase.) I didn't check what her age was before, but because I have had her for longer then 16 years, I am quite sure the age does not reflect 'real' age in-game.
Because I've had that one for so long, and another for sure too, I believe the kittens do not die of old age. Luckily, otherwise the skills would reset every time a kitten die of old age.
update: Year 96, and Lily Paws is still a sixteen year old farmer. Only change is the skills: she is now 25% proficient.
update 2 Furthermore, In the village.jsthere is the following line:
this.age = 16 + this.rand(30);
when the new kitten is constructed (alongside with the creation of the name). In the rest of the code I cannot find anything where this age does anything at all.
update 3 Year 152. Lily Paws is still a sixteen year old girl, enslaved on my farm. Evil laugh
update 4 Year 202. I think I can confirm that Lily Paws is immortal. She is still busy on the farm. She mastered the job though, so she has that going for her, which is nice.
update 5 Year 327. Anyone doubting the immortality of Lily Paws is an idiot. She still is a 16 year old. Possibly sucks the blood out of innocent canines in the neighborhood.
That's all you need to do. Click the save button, then refresh the page. As long as you have javascript enabled (I didn't, and gave myself a heart attack when I refreshed), it'll find your save game, and you're off to the races.
Best Answer
There is no end to Kittens Game.
Some of the far off things to achieve in the game include the Cathammer 40k achievement, requiring you to play for 40,000 years. So you still have a bit to go.
The Unobtainium you got is actually only the basis to an even rarer resource, Eludium. It is extremely expensive to produce and can be used to construct certain space structures and research high-end workshop upgrades. Additionally, it can be used to trade with the Leviathans, your most important trading partners during the late-game. They will provide you with resources which are even rarer than eludium and can otherwise only be obtained by massive unicorn production.
To make contact with the leviathans, you need to construct Markers and Black Pyramids.
Also at later stages of the game, Religion plays a huge part, as it grants you extensive production bonuses. You will reset your faith counter often to get a praying bonus, which will lead you to accumulate even more faith and larger bonuses. This is known as the Apocrypha bonus.
Even further, you can sacrifice your apocrypha bonus, by transcending, which is a technology researched late in the game. This opens up even more advanced religion upgrades.
In addition to that, you have the normal game resets, which grant you additional Paragon (among other bonuses). These can be spent on Metaphysics upgrades, some of which are required to open up technology paths otherwise unavailable by non-reset gameplay (as you only earn paragon at a very low rate, 1 paragon every 1,000 years). This will enable you to build the markers and black pyramids mentioned earlier.
Beyond that, there are extremely expensive technologies which currently have no purpose. Their purpose is still to be decided and will be added in later updates to the game; these technologies include Thorium and Terraforming.
It is my understanding that current development focuses on giving more purpose to the Darkmatter resource, a resource that was only recently added to the game.