“...where/when do you draw the line?"
When you hear the little voice.
Last year, I put away a lifelong passion. I was not reluctant, but less likely to take a sportbike on a commute, a trip, a fun ride... As the bike got less attention, the reactions, insights, performance, and capabilities built over years of saddle time, decreased, and the little voice reminded me I was not "as good as I was."
Like a GA pilot, I took recurring formal training to get a third party objective and endorsement: I was still safe, current, and competent.
Riding at a high level kept me focused on getting better every ride: examining brakepoints, turn-in, lean angle, shifting, timing, positioning...
The difficulty, and the consequences of a mistake at speed, made me work at "better" every ride: examining brakepoints, turn-in, lean angle, shifting, timing, positioning...
I did not want to get hurt, much less hurt a passenger (rider, pedestrian, driver...) from my error.
When I heard the little voice, I listened, and listed the bike.
The last "Condition Inspection" was telling.
Cleaning -for years a joy - was more work; using special tools now took time to find what had been proud exhibits; crawling to check the bottom of fenders, frame, and suspension was a bit slower; and the logs and manuals took time to re-find.
After some searching, I met a busy, energetic, enthusiastic, less-experienced rider, and a sale became mentoring and helping someone step up to a new challenge.
Just as I've been "happy to be down here, wishing I was up there" a time or two, I'm happy to be off two wheels by my choice.