A good topic, filled with various points of view. I would like to add a few from my POV. First, I have raced against Porsche 911s. I have in the past beat them every time. There are 911s out there that can go very fast. Sterling Moss used to be able to drive a Volkswagen about as fast as many amateurs can drive a 911 on a race track. If you are going to drive very fast on a race track though you'd better have a fast car. The adage in racing is "Speed costs, how fast do you want to go?" Another reality is that if your are going to be a pro race driver you must start fairly young or you never are going to race say Formula 1 with other pros. I have driven Porsche 931s which are way faster than a 911. A Porsche 962 would be a very difficult car to race against without a very tricked out high performance and mega-expensive ride. That is why there are classes in every major race like 24 Hour LeMans. I have raced GT class. I never knew a SINGLE older person who really made it in racing. Ferrari is only one brand of race car, but a very good one. To date me Chevrolet Chaparral was a very effective Can Am car. Ford (the Ford GT) had a very good one. Carrol Shelby (the Cobra) had another, etc..
On to CAMERAS. I knew Ansel Adams and he would have been a good photographer with a D800 Nikon. But with 8x10 things are quite different. I never had the pleasure of knowing the famous William Henry Jackson, initially from the William Brady group of photographers on the Civil War team. The US Post Office had a very nice series on these influential photographers and the commemorative jacket for the series featured WH Jackson in Yosemite on the Balancing Rock overlooking the main valley from up by Lookout Point.
I know teenagers who have been given Nikon D800s. One is very well known by my son and grandson's who are also really into photography. My son is making a personal trip to B&H just to see the place for his first time today. I asked him to look at the D800 and see what he thought. We use D7000 a lot and a lot of DX Nikons and owned a D700 which I sold but always wonder about that as I actually rarely sell my cameras just seem to keep them as milestones but when I was with large and medium formats I decided to Sell them ALL after becoming convinced that 35mm was far superior in field work. Digital is far better for us to work with here than film ever was.
What does AGE have to do with it?? Almost everything it seems to me. Younger people seem to thing video is the standard. Feature movies are very influential in our lives. Problem start when you try to match a movie much up the ladder from home movies. Editing, storage, gear, etc. becomes a very large investment. But there are young people who think of photos as pretty much stills first and foremost. Field photography becomes really a challenge for the old. I knew a large format pro who had young people carry his 8x10 gear but in awhile his 8x10 work became roadside shots as he couldn't get someone to carry him up to the high peaks. I had photo ops as a young man I will never have today, partly just based on age. But another aspect of age is that if you are say from 70 or older you only have so many years to continue active work.
What does age have to do with DX versus FX DSLRs? Less for sure. Excepting the all important Cost of Entry. I think FX is for wealthier people as a gross generalization. But Nikon D4s are very CHEAP compared to quite a few other pursuits. One of the things NIKON had better damn well be considering is age of entry into this work or hobby. If you look at an industry and it is entirely populated by older craftsmen then it is likely on the way out. I had a very large exposure to economics on a national and international scale and if you look at an industry I think you'd better begin looking at what age are the participants pretty quickly. DX Nikons very likely are the better entry point for many today.
To look at Nikon's latest offerings (except the D5200) you'd never know this. I know no less than 50 younger people who got their FIRST DSLR camera this Thanksgiving (and they think of it as a Christmas purchase too). NOT ONE got a FX Nikon. Most of them got a D7000 and many where still considering a D90 which i admire but I think the D7000 is more up to date. Almost everyone also wanted a good a video on board as possible. I conclude from this DX is a more affordable format and right now a better entry route.
If you don't think the route someone enters better format cameras (usually now from iPhones) to DSLRs then you and I would disagree there.
Again there are some really excellent points of view in this thread and GOOD Luck to You ALL.