It´s amazing how good you already are at the age of 16.
I didn´t know any of this or was interested in anatomy when I was years older than you.
Very good
You got some very good advice from the other members already.
When I could turn back time and start again I would approach figure drawing like that:
-first step perspective, this may sound weird to you because most people connect perspective
with backgrounds but you need perspective for figure drawing
-gesture / line of action, you can easily train that with quick sketches, it becomes fun after some
time, focus on only the form, no details, no muscles yet
-then form and shape, learn to draw in the ribcage, pelvis, head, arms, legs in perspective
with simple shapes
When your figures look good then it´s time to learn anatomy, insertion of the muscles, function
etc and it will be easy for you when you followed the first steps
It´s really great that you are already so good at your age, don´t forget the fun