Ok, as fredob requested, this is an n=1 style of writeup, for my experiences and what I consider to be the core kernels of a lifetime fitness program. Note, this is not a design for specific competition, this is fitness in general. Obviously if you compete, you would need to tweak the physical component and nutrition components to support that.
This is the first component, and arguably the most important. You can be running 75 miles a week, throwing around heavy weights, whatever your activity might be, but shoveling big macs and fries down 4 days a week with pizza and ice cream chasers. If you don't supply your body in a healthy way, you can't expect it to perform consistently. Note I say nutrition, and not diet. In my mind, diet implies a process. The problem with a process is that it has a beginning, and an end. There is no end. You either have good nutrition planning or you don't. Doesn't mean that you can't have cheat days, fall of the wagon a bit, etc., but overall your nutrition plan is sound and based in your needs for daily existence plus your activity.
This is the second component. Protect your mind. Play games, play an instrument, read a book, do puzzles, whatever floats your boat. Keeping your mind active and well rounded will enable you to still be sharp and on top of things well into your twilight years. The more active you can be, the better.
Get out. Do SOMETHING. Walk, ride a bike, swim, play horseshoes, move around, anything. Get your heart rate up, sweat a little, make your body work. Find something you truly enjoy doing, because like a diet, "getting in shape" or doing something you don't like for the sake of activity is a dead end process. Ok, so you got in shape. Now what? But, if you truly enjoy what you're doing, you'll keep on doing it.
More and more, studies are showing that resistance training can help preserve muscle as we age. Take a look at what you do in your physical activity, and plan your resistance training to supplement that, and keep your muscles in balance. A lot of back problems, for instance, could be alleviated if people trained their spinal muscles as much as their trophy abs. You don't necessarily have to heave around small cars, but especially as you age, resistance training can help preserve muscle.
Keep your life in balance. Make time for your sports, family, work, personal time, etc. When you start sacrificing one for the other, your life eventually starts spinning out of control. There will be times when you HAVE to sacrifice for a bit, but let those be as short as possible.
Now, I have been in sports for 41 years. This includes 17 years swimming, 9 years cross country (HS/College), 2 years wrestling, 4 years competitive cycling, almost 20 years in martial arts. I've competed at every level from local clubs to a handful of Nationals and a couple of Worlds. As soon as something stops being fun, I find something else. (I walked out on two years of scholarship in swimming because I was burned out. Still hate swimming.) I play D&D, board games, poker, chess. I have an outstanding wife and wonderful family. I recognize my capabilities, and I'm still not sure if I've found my limits or not.
In those 41 years, I've had one injury (Ruptured achilles 6 weeks ago) that kept me sidelined for more than a week. I attribute this to a lifetime of athletics, lucky genetics, and enough sense to monitor myself and sensibly push my limits, and staying within the above categories.
Hope this is what you were looking for.