It's very simple, they say. All you have to do is:
Yeah, yeah, yadda, yadda, be strong, conditioned, blah, blah.
What they don't tell you, or maybe they don't know, is there are some "mud puddles" that can take you down on any ride.
Having your "stomach shut down" is a real "killer".
Suddenly, you become
All in all, a bummer.
There are bunches of other things that can wipe you out, but those 5 are nasty, show-stoppers!
If you think about them (and you're over 40) you'll realize that for long rides, you better not try to "burn fat". Sure the "kids" can do it and still ride as fast as you, but most folk find 8-10 mph to be a bit tedious/nonsensical for riding 200 miles in 16 hours.
So, how did I figure all this out?
I was lucky enough to vacation on the Big Island of Hawaii and was able to try to ride the Iron Man route from Kailua Kona to Hawi (actually, eventually, the Pololu Valley "end of the road")
Everything you would want,
if you really, really want to and enjoy riding 100 miles or more.