>Having done both, playing complex board games and card games is not nearly as complicated and engaging for the mind as a full time customer facing job

I think one should optimize for 'most intrinsically rewarding' not 'most engaging'. I shudder to picture a retirement spent doing 'customer service' and if a retirement of working on projects, travel, reading and playing video games leads to 'more cognitive decline', well, so be it. I would rather be daft in my old age than miserable