HOLD MY WATER
I have a file... somewhere.... that shows.... mine... digs through files frantically
I use an excel sheet to keep track of dates (approximates) and ages. It's a calendar that has stuff for the world and timeline but not all stuff that will effect the story. For example, this part shows the birth of an important character named Matéas.
As time passes I manually keep track of ages and things happening to a degree.
(different colors indicate a different 'age' since Mateas lives a long time, he goes through several 'calendars')
Now if I had set it up differently I'd be able to have the year numbers in a different tab and use excel to just do the math for me (by writing out the equation: X=2470+524 for example). Instead I had to do the math myself.
I have a physical note somewhere from the start of NTN where I have arrows and lists of things that basically are things like Will-> son of Adell & Laeri -> Adell's married to Mia -> has son Alexander with her.
It ends up looking something like this chart
I'm pretty sure there's a few programs that you can do this stuff on. I think I'm thinking of Scrinver but some people use personal wiki's to do the job
https://www.gaiaonline.com/forum/writers/t.103605989_4/#4