Why do I have to "grow" into a managerial role? I like doing what I am doing and would like to do it more. Anyone with some serious advice on how to stay relevant in software development with greying hair and without growing into people management?

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Architect ?

Because only when you become incompetent do you get moved into management (there are rare exceptions)

There are fewer hard-tech positions (architect/lead/whatever) than trench developers in larger companies. Some companies just plan on funneling most devs up into management, promoting the wizards into architect roles, and back filling the trenches with up-and-coming talent.
My employer has 4 people on software, I anticipate getting to keep my hands on the code for some time.
Talk with your current manager about what your career trajectory would look like if you declined promotion into management. The answer may surprise you, or it may encourage you to jump ship.