I am not so sure fasting reduces IGF1, in facts raises HGH which in turn raises IGF1 since the two are tightly correlated.
Anyway if you aren't involved in a car crash, get a heart attack or cancer chances are you'll fall while safely inside your home, break the femur, get hospitalized, catch a nasty bacteria while there and goodbye...
That's how it goes for most... therefore, in practice, an healthy IGF1 level is likely your best beat in order to live longer.
Take 100 people of the same age, lets say 60 years old, now look at them, do all look the same (age wise)?
Of course not, some will look younger while others will look older.
If we try to find a reason why likely we fail, yes, maybe on much bigger numbers we'll find statistics telling certain lifestyles are kind of predominant but there will be always a good number that don't fit in the equation but still look much younger (or much older).
So what?
Well, obviously there are factors going beyond lifestyle, epigenetics play a big role but genetics does too... and possibly there is more than just those two.
You don't know how you would have aged following a different lifestyle, maybe you feel what you have done played an awesome role in keeping you looking much younger than your actual age but maybe it is totally irrelevant since a whole different lifestyle would have yielded the same results, it is just that you age that way, period.
Or maybe you feel like in despite of all your efforts you are aging as everybody else but maybe if you didn't take care of yourself now you'll look much worst since your predisposition to graceful aging is poor and your efforts actually did make a difference.
It is quite impossible to tell, really.
My take is do the best you can which you feel comfortable with, at worst you'll have no regrets to worry about.