Bro all you need is time and YT Vids… they give good advice for anatomy. Then again if you look at my art then you wouldn’t believe me but I am just lazy ngl.

I don't get how these people do that, they're surnatural to me
Learn bit by bit, and never forget to be proud of every little victory! One thing at a time, switch to something else when you're tired of repeating! Yeah repeating's the key, and yeah it's super tiring, so take it easy
Here i'm just dropping little advices here and there, don't see my experience as universal cuz i'm just a small cartoon artist, still trying hard to learn anatomy at 18 x)
AGE DOESN'T MATTER!

I'm not that good at anatomy (all my poses are static as fu*k) and i'm no art book expert but "Figure It Out! Drawing Essential Poses" by Christopher Hart is really helpful, if you're looking for a more cartoony look with exaggerated proportions, there's also a cartoon anatomy book also made by Chris Hart (both of them are like 20 bucks so either suck up to ur parents or save up)

Anatomy is the art of SQUARES(my case)
Embrace squares abandon reality (⁠✷⁠‿⁠✷⁠)