How long do you or should you keep your gear.

And to you to sir Happy New Year.

I still have my Pioneer SX-750 that I bought new in 1976.

Early in my pursuit of a high end system it was a ongoing effort. But as my system got better and my income increased listening to music became more common and upgrading became episodic. Over the last couple decades it has been upgrade about every seven years. 
 

When you own true audiophile components then it is really 7 - 10 years to get a “wow” from an new similar component. 

Don’t know yet. College system stayed with me from the late eighties through last year when I decided to do a ’small’ upgrade. From April 2020 to date, the entire old system disappeared into the basement, the components of my new system have changed twice and I built a back-up/office system. Seems to me that barring a couple of ’better’ power cords these systems are finished. I like ’em.

Depends on the gear.