A guide on how to customize your paras’ life stages to your liking.
Introduction
I will guide you through making a lifespan mod, and fear not, if you aren’t a modder, because this is really just game configuration with a few extra steps. I believe in you, you can do it. Just follow these steps, and you’ll have yourself a custom lifespan in no time.
Setup

Emphasis: Ensure you do not have any lifespan mods installed!
Once you’ve made sure of that, you’re in the clear to make your own. On the bottom right of your screen, you’ll see the Create New Mod button. Select that.

You’ll be prompted to give it a name. If this is only for you, name it whatever you want, but do give it a name you can live with if you intend to share or publish it. They seem to have fixed the issue where the name field was unclickable if you tried to rename a mod, but I wouldn’t chance it.
If you do intend to share it or just want it to look good, you can give it a description and add a cover image to it. There’s no need to do it immediately, and could always be done later. That part is genuinely just up to you.
Configuring Your Paras’ Lifespan

Starting to edit a mod will trigger a loading screen. This is normal, just wait it out. Once it’s done, it’ll just return you to the same page (My Mods). The only difference is that, with editing enabled, the button on your mod will instead read Stop editing this mod, and all other mods will be blocked off.
Now that editing for your new mod is enabled, you’ll want to go to the Control Panel, where the game settings are. Anything you edit there will become part of your mod, so don’t touch anything else for now.

This will take you to a screen featuring a lot of modding options, though we only need one for this. Now, there are two ways to get to the option you need. You could just scroll down to the Personality and Identity category and select Life Stages from the list there, or you could click the magnifying glass icon to open the search bar and type “Life Stages”, which will remove every other option (though you will still see the other categories, as if collapsed/empty). Regardless of how you got there, you will now select the Life Stages option.

Here comes the fun part. You will see many collapsible options, with all life stages being under the predictably named All Life Stages category. Here, you will see options for everything from HumanBaby to HumanElder.

You’ll need to input lifespan durations into each one individually. Since we’re only here to set up your preferred lifespans, don’t touch anything else, only the options under the Duration category, which will be Start Age and Stage Duration in Minutes. The first one is an single line you can input a number into, while the second one is split into days, hours, and minutes.

This part is up to you, since you’ll be making each lifespan last however long you want. For Start Age, whether you make changes depends on if you’re satisfied with how the ages are divided. For example, with default settings, toddlers begin as 2 year olds, children as 5 year olds, preteens as 9 year olds, etc. You only need to change this (for any category) if you want your paras to be a different age upon first reaching the stage.
The more important part is Stage Duration in Minutes, since that’s what actually controls the lifespan itself, stage by stage. Since you can tune it down to the minute, the world is your oyster, set it up however you want.
Once you’re done with that, you’ll have done everything needed for the changes themselves, assuming everything is in order.
(Optional) Configuring the lifespan options
These options are what you see when you are customizing your storyteller, and what they do is apply a multiplier to the duration of life stages. They’re just multiplied by 1 when set to Normal (so, no change), but Short and Long lifespans multiply them by 0.5 and 4, respectively.
You can change those if you want, or create a new option outright by pressing the + button. If you choose to do the latter, you’ll need to give it a Display Name and set the Stage Duration in Minutes Multiplier.

For the name, make sure you click the Translate icon next to the input bar, which will prompt you to set the Translated text. That will be what the setting you’ve made is actually named.
Again, that part is optional, so don’t worry if you stopped at setting the duration of each life stage and skipped this.
Testing your new lifespans

Finally, close the game. You need to make sure your new mod is loaded before testing it, and just being on the menu won’t cut it. Close the game, and launch it all over again.
Now, why do you need to test? Because, for the love of all that is good, never put an untested mod into any save files you care about, especially not one that edits something as significant as this. Make a new save file for testing this before you actually use it.
For lifespans, what I usually do to test is make one para of every age in the paramaker and place them in a lot. Since there are conveniently eight life stages, these eight paras are enough to check if the changes are working, all with minimal effort.

For each of these test paras, open their profile.

To the right of their personality level and beneath their name, you will see the lifespan progress bar for your para. Hover over it and it’ll tell you how many days they have left in their current life stage. Check all your test paras for this, and make sure the numbers you see match what you set when you configure the lifespan. Since you’re testing with freshly made paras, their progress bar will be nearly at the bottom, and they shouldn’t be any older than perhaps 1 day into the stage.
Unless there is a conflict because you forgot to remove another lifespan mod, the values should all be what you set.