I too have a work colleague who went from supposedly nothing wrong, looking forward to Xmas, to having a brain tumour.
I'm approaching 50 (June 2020) and in the past few years, have really woken up to the fact, that we aren't immortal. We don't know what our future holds, but I'm hoping to be able to retire in my mid 50's, because I want to be able to live life to the full while I'm still able bodied and strong enough and not to be tied down to having to get up for work, but to get out there and see and do stuff.
I urge anyone reading this even in their 20's and 30's to start to get out their and enjoy life, but also think about later life and start to prepare. By the time you get to 50, you'll not be able to claim a pension from the government at all, the way things seem to be going. Do you really want to be at somebody's beck and call and being tied into working in your 60's and 70's.