>>7783751 (OP)
>>7783758
If you study at an atelier (which is much cheaper than going to university) you can learn to draw figures like that accurately from observation in a year or less. Of course, it depends on your prior experience, talent, etc., but the method is very well established and even total beginners will see progress under a competent instructor if they stick with it.
Drawing figures from imagination is something else entirely and requires a different track. The method of observational drawing taught in ateliers treats the subject at the outset as nothing more than dark and light shapes to be carefully measured and then refined, working from the largest and most enveloping shapes down to the small details. Anything you learn about the figure from this process is incidental. The approach is not anatomical or structural, although most ateliers do offer separate classes in artistic anatomy.
Inventing figures from imagination is harder and takes more time to master because it calls upon a much larger skillset than observational drawing. You have to be familiar with average or ideal proportions, anatomy, function of the joints, range of motion, basic perspective and how to draw and render primitive solids like cylinders, cubes and spheres — and then there are more advanced topics like rhythm, dynamism, composition, characterization, etc.
