Old age and retirement

As I grow older I've been fascinated with retirement and 'old age'. I mean what is old age and what is expected of those who have retired. The norm seems to be people retiring and spend time visiting children and grandchildren or help raise them. However in this day and age this has really changed. For starters what is old age? We seem to think that old age is when people retire or stop working which is around 60 to 65! Retired folk that I know are fit, robust people. There's a study floating around  that found people died shortly after retiring and it is suspected that it's due to boredom and depression from change of routine and not feeling needed. 

Looking around me at all the sixty plus year olds, I find highly unfair that retirement is forced upon them. It's unfair that age seems to determine people's usability(?). My mother has hit seventy and is fit, robust and a hard working woman. Somehow retiring or ceasing to work does not fit into her vocabulary. My dreamy view of grandma travelling around the world visiting her grandchildren seem selfish and just that: dreamy. My mother enjoys her work and helping people and one can never stop helping others! My mother does visit her grandchildren when she's on one of her work trips! The same goes for my parents in-law. They are hard working people past their sixties and they are very good at what they do and manage to fit family into their working lives.
Two of hubby's colleagues retired last year and those two men were at the top of their game. One was a trainer and both had over forty years of flying under their belts and it just seemed so unfair for these men to stop flying when they were both of sound mind and hadn't had incidents at work and could fly better than many others around! The retirement age should be reviewed case by case. Retired folks are said to drain the social system in certain countries due to many living in to their nineties...so why force them to stop doing something they love to do while earning a living as well? 
I'm working on changing my view of the future as living until I check out but not seeing a certain age as the finish line or slow down lane. I have a lot of respect for people that have retired and are still making the most of life and have not slowed down due to age. Obviously it's different when one has an ailment that forces them otherwise.