Hi,
I normally don't respond to posts, just gather advice from them - but your post today struck a cord. I usually try to go 'all out' in races and generally have good results. But after thinking about it, I have not reached the point of nausea and throwing up, which I used to do all the time, in quite a while. My training is quite intense and really hasn't changed much over the years either.
I think you are right, as we age we (should) get smarter. Why push ourselves that hard when it hurts

? Come on - throwing up just isn't fun! I actually ran the fat ass 'for fun' and what a different experience! I ran 17.5k, barely broke a sweat, and carried on the rest of the day with no pain (other than being cold and wet until I got home). I did the 1/2 at PEC running as hard as I can, and I was toast the rest of the day. So yes, I think as we age we are getting smarter!
Mitch.