So...is there a general age or number of hours where one can expect to have this issue?

IMO
Probably not, it depends on how the drive is used, how much HP, and what lube
Have not heard where its a bad problem, just happens every so often

You can get the plastic gauge for shift cable adjustment from MerCruiser Tools and Supplies for the do-it-yourselfer really cheap. I keep it in my toolbox on the boat. They have improved the cable design, if you have an older drive, it may be worth getting a new cable. I was having similar problems and it was the cable.

Thank you for the info. I looked and didn’t see a shift cable gauge tool. Do you know what it’s called? Thanks much.

The last couple of shift cables I've installed didn't need the tool because the cable was preadjusted 91-17262

Thank you

Thank you sir.