4) Stay fit and at a consistent weight to avoid ending up like my Mum who was overweight for most of her life and now in retirement can barely walk, is depressed, has alcohol issues
I think this is the main thing about fitness, that it enhances the quality of life rather than perhaps extending it greatly.
To be honest it pisses me off a bit when I see sedentary and morbidly obese people living as long as fit, "healthy" people.
I think I should expect to live at least twice as long as someone like Cyril Smith, but the sick bastard lived to 82. 164 years old doesn't seem unreasonable when you compare our lifestyles.
However I think it's all about those final 20 years and the quality you can expect. Sure, I know some cyclists who die, mid-ride, in their 70s and 80s . That seems unfair until you realise they were cycling in their 70s and 80s, not tied to an oxygen cylinder in their front room.
In 50 years (or maybe today) I can see that the UK will have an enormous issue with people in their 70s and 80s who may not have been able to walk for the past 20 years of their lives, never mind cycle 200km.
The incredible rise of "Moby-Scoots", far from giving people back their mobility, are robbing them of it, from an early age. We have a WIMPY Burger joint in town, it looks like a Mobility Scooter dealership outside. I assume the only exercise these people get is walking from their Scooter to the counter, to order their burger-fries.
Note. I've heard them referred to as "Obescycles".
So, from a life-expectancy point of view, I expect I'll do as well as my Mum, Dad, Grand-Mothers & Grand-Fathers on average (Actuarial Tables say that the best way to increase life-expectancy is to choose your parents carefully) and that all I can really do is to make the intervening years as good as possible, avoiding the mobility-scooter and Oxygen cylinder for as long as possible.
To that end I think I'll focus on a sensible mixed diet (all research seems to point to "eat a varied diet, in moderation"), a fair amount of cycling and a bit of swimming.
I've found it takes a disproportionate amount of exercise to lose the same weight as cutting back on the calories but this is about being lighter, slimmer
AND fitter.