I'd say as one ages one develops a more realistic understanding of the dangers & the long term consequences. This brings with it increased caution.
A young adult feels invincible...you lose that feeling round about the mid-twenties (sometimes earlier) and that is a bit frightening. It'll go away - it'll require a bit of introspection though. The exact nature of that path will depend on your religious/philosophical outlook,
Too true, my doctor once said that it is common to find patients quite shocked on learning of their illnesses.
The feeling of 'invincibility' in health matters is quite common, like so many things in life - stuff happens to 'other' people.
Agree with Hemi - with age comes wisdom (though this is not a rule)