Okay.You've got 17 hours for the whole race. 2 hours 20 minutes for the 2.4 mile swim. That leaves you less than 8 hours for the 112 mile bike and another 7 hours to get through the marathon 26.2 run/walk/run/crawl/run.
Everyone says I'm crazy to even think of it.
Sure, it's crazy. That's one good reason to do it. And fun. Really fun.
There must be some reasons not to do it.
Aside from physical disabilities, family obligations can be a serious deterrent. Not good to neglect the kids and leave the spouse home alone. Choose nearby vacation spots for your races and spend extra days there. Go on hikes and you run back and forth. Get the little ones on tricycles to pedal along beside you when you're running. Tell them what you're doing.
Now tell me why I should.
It's satisfyingly extreme. The people are supportive. Everyone has a weak link, so you'll be good at something. It does not have the tension of shorter races because the emphasis is on endurance. Go for it!
So.... how do I get started?
The RUN is the simplest.
3 times per week, run a comfortable distance. Walk back half-way, run the rest. Once per week, run as far as you can, again walking back until you think you can resume running for rest of the distance. Increase as you are able.
The BIKE is equally straightforward. Find friend or family to accompany you. Also, 3 short rides during the week and an increasing long one on the weekend.