Don't really know what age HRT is required, but a local lady runner aged 45-49 has qualified to run with the elites in London 2 years running now - so there may be something in your theory....
Know what you mean about the shorter races - just ran a half marathon for a bit of fun at the weekend with very little training - but really enjoyed it and equalled my PB!
Mind you, I went there to be anonymous (as I was expecting to be embarrassingly slow) - until my competitive running partner saw someone they knew (but are not particularly fond of) and demanded that I beat them! Ruined the start for me as I'm not particularly competitive (only with my own times) and I sulked big-style that I wasn't going to be able to just relax and plod round, using it as a bit of training.
Anyway, it all worked out ok and I really enjoyed the run - not much wind (for a change!) and flat.
But for the first time in a few years my focus has moved away from Disney - to Rome! Really excited about going now - another 20th anniversary medal!
I dare say that immediately after Rome I will be dreaming about the 10th anniversary Goofy.....