Indeed, and not just triathlon training. I'm by no means extreme, I just try to do an hour of exercise per day, but I do look enviously at my peers also in their 40s who don't exercise and so have lots of time every week to do 'fun' stuff.

To the time required for exercise has to be added all the preparing of kit, travelling to pool etc I was up at 05:45 today and have just been able to start breakfast at 07:30. Oftentimes I wonder if it's worth it.

I've had two periods of "intense health" so far. The first was high school through college where I was racing and training year-round. The second was in my mid-late thirties when I had a "full time" job that wasn't terribly busy, and I had kids. I definitely think that the job has a lot to do with it, but geography does too. I move around a lot and can tell you it is much easier to train in San Diego than it is in New Orleans or Norfolk, Virginia. Another key element has been friends to exercise with.

I may be entering a third phase with another job transition which came with a move to a new location with world-class diving opportunities and readily accessible pools with lap lanes, despite working about as many hours as I did at my last job where exercise was next to non-existent simply because of commute time.

Wouldn't this be more true for middle aged though. I certainly had way more time in my 20's.

I guess it depends on your definition of "middle aged". They seem to be talking about people in their late 40s to early 50s who you'd expect to have grown-up (or at least high-school aged) children and a lot more free time, compared with 30-soemthings with small children.