Running through some code here and keep seeing other entrenched programmers writing monstrous 150 line methods that are void typed.  WHY?!

See here for more detail:

https://martinfowler.com/bliki/FunctionLength.html

The longer the function the closer it becomes to unmaintainable because the more lines you write the more complexity is encapsulated in a method and the more things you must check or verify.

Some Functional programming tries to sidestep this with continuations of data, but that can get overly long as well.

Recommendations dependent on verboseness of a language, but 20 lines or less for C type languages and do not go over the 80 characters per line if possible.