Coming in late as usual, I don't have too much to add to what has already been said. ALL aspects of life must be looked at to insure health and longevity. We tend to focus on the exercise and nutrition components here, but the stress reduction and sleep factors are huge.
I don't think genetics play too big of a part in when we check out. Some, for sure, but we really do have control. Looking back to those hard drinking, smoking individuals who live to an old age - what might they have been doing right? Perhaps a very low stress life? Ate crap food, but got plenty of good sleep?
Re: seasonal training - pretty much as Robb described. Low carb + IF 7-9 months thru the winter, doing strength, skill, and movement work + 1-2 metcons. For 3-4 months in the summer, more frequent metcons, maintenance or low volume strength, and higher carbs.
I'd highly recommend movement health and mobility work for health and longevity training as well. One of the simplest ways to judge the average person's age is to simply observe how they move.