First, you'd have to define "elite fitness", I suppose. Navy Seals? Olympic-level decathletes?
Top level triathletes? "Ultra-marathoners"?
Bodies are so different in physical makeup and construction this would be a difficult chore. Folks who are blessed with lots of fast-twitch muscle fiber can train to become very good sprinters and weight-lifters and such, but will never excel at endurance activities.
Look at the pro cyclists. The team sprinters struggle and die in the mountains; many actually abandon the race when the mountain stages start. Yet they can outstrip everyone in that last kilometer......
If you are blessed with lots of slow-twitch muscle fiber, you can become a great marathoner or triathlete; you might swim the English Channel or win the Tour De France...
But you will never become a power-lifter or a top sprinter.
Most folks have a pretty even distribution of both, and can become "the best they can be" at both strength and endurance activities.
Other factors... Physical construction. Long, lean... Long arms and legs? You might do well at a variety of sports activities.
Shorter, more heavily built? Relatively short limb length? You might be a good competitive lifter, wrestler, or whatever... Unlikely you'll excel in sprints or basketball...
To my way of thinking, if you are not a high-level competitive athlete or pro, then attaining "elite" levels of fitness is almost verging on a species of obsessive-compulsive disorder.
You have to spend inordinate amounts of time in the process, and factor in diet and rest periods and everything else in addition to your working life.
And for most, this is a very transient sort of condition. Age, injury, life-circumstance change... These things can all cut your training severely.
As I've gotten older, I'm quite content with a "pretty good" level of fitness. I do my resistance exercise and I ride my bike for the most part. I'm at a decent BMI, my lipid levels are good, and I'm fit enough to do my job.
