Most of my basic conceptions of how river channel patterns work is
based on some simple, yet insightful diagrams created by Stanley A.
Schumm, a leading thinker in fluvial geomorphology. The two figures in
this post are some well known renditions that he published in several
forms and venues over the last few decades.

Throw 'youth' , 'maturity' , and 'old age' out the freaking window.
Rivers do what they do in response to imposed sediment discharge and
calibre; fluid discharge; and local and regional boundary conditions
(think climate, lithology, tectonics).

Teach it that way to students. Introduce them to the factor of time in
the context of how channels evolve and vary over time in response to
changes in the various controlling variables. Emphasize how they
metamorphose through a continuum of patterns over time.