I currently am doing something very similar, and I feel pretty strongly that I could literally do this until I die, just like I plan to do my music gigs until I die.
Literally, I am billing < 20 hours a week, and unless I become disabled and/or get dementia/Alzheimers, I feel that I will like doing what I am doing in some form or other forever.
I've done a lot of different things in my life, and this _is_ having it nice. It's far nicer than the "retirements" of many of my friends in their 70s, though I will grant it is not as plush or completely free of pressure as my parents' retirements as school teachers/administrators.
