At what point do we begin to respect the opinions, knowledge, and experience of a service member?

The next great idea can come from anywhere, and anyone. Heck, if anything, listen to the young ones before institutionalization kills their creativity and they're assimilated into the collective. (You assumed there would be no Borg reference in your life today.... you were sadly mistaken)

Depends on the situation and Soldier. I can think of several junior Soldiers that I welcomed their input and suggestions because they had proven to be honest, respectful and proficient. Conversely there were a couple senior NCO's I wouldn't take their word if I was standing next to them when something happened, because they had lied about inconsequential things or passed the buck on their troops instead of taking the heat.

This is very much dependent on the situation. A brand new PFC might not offer much from a combat perspective but may be well versed in other important areas. Likewise, a grizzled veteran may know the ins and outs of combat but no nothing when it comes to non-combat things. With that said though, guys who have "been there and done that" tend to get the benefit of the doubt over those who haven't. That's just life. There isn't always time to interview everyone in every situation to judge their expertise on a given scenario.