I would define a population as being healthy no different than the medical profession looks at a human population as healthy or not. If the individuals within the population display a normal or low incidence of maladies i.e. disease, genetic disorders, nutritional deficiency and also display other physical characteristics within the normal range for their age e.g. weight I would consider the herd healthy.
Age is not a criteria for health. You can have healthy 5 1/2 year olds and you can have unhealthy fawns. A herd where the average age is 2 1/2 can be just as healthy or unhealthy as a herd where the average age is 1 1/2. The incidence of maladies is the indicator.
Please talk about spontaneous abortions of does
Fawn mortaility, nutrition, the yearling age class or less and death associated with starvation as well as the effects of two or even three ruts and the nutritional ramifications this has on the herd.
I've addressed most of these above and would agree that if there were a high incidence of fawn mortality or malnourished individuals then the herd would be unhealthy. Age structure of the herd or the number of "ruts" that occur each year are not health criteria. You can argue that both of these may impact the health of the herd. That's certainly a legitamate argument but they are not by themselves measures of health.You can't just say the average age of bucks in the herd is X so therefore the herd is not healthy. You can't just say the herd is having X number of ruts therefore the herd is not healthy.