If you are talking about general demographics (similar to what Google Analytics provides) there is nothing... GA is a glorified guess... you might as well attribute a users gender to where a few darts lands on an "age" dartboard, and on a "gender" dartboard... A few years ago, you could check what Google thought it knew about you... there was a reddit discussion where everyone was laughing at how off the information was.....
Now, if you have users providing that information into their accounts on your site, and have a privacy policy about how the information is being used, then you can create dimensions (note that all dimensions store as text, so even with age, you won't be able to create segments like "greater than X" or "between X and Y", you could use classifications and regex to create buckets that you can create segments on)
In launch, you could also use JS to process ages into buckets and track those, but if you have to change the buckets, it will require a code change in Launch.
Now, I am going to assume you know how to add new Props or eVars in your Admin settings for the suite (otherwise I expect this post would be a more generic "how do I create a new eVar to use in my implementation")
So is your question about how to get the age and gender from your user accounts into your tracking? You would have to work with your developers to make that information available to you.. depending on your site, they might exist in cookies or session storage variables, which you could access immediately.. or you might need to have this information added to a Data Layer that you can read and add to your tracking.
The other option is to map User Data to a User ID through Customer Attributes.. I've never done this, but I saw a webinar about it about 10 years ago... You could look into that.. this way you aren't collecting the data directly, but stitching the data from your backend user data....