In my opinion…
Question Number #1:
Being a leader and having experience are two different qualities. A good leader discovers, respects, and uses the experience of his team. If you want the team member to respect your leadership, then respect his experience.
A good leader doesn’t make all the decisions without any team input. A good leader let’s the team make many of the decisions. The team will feel more involved and excited about the task at hand. The leader’s role during the team discussions is to drive the team towards a goal and mediate as necessary.
I do see your question has concerns to the difference in age. You can’t control what you can’t change. So unless you have a time machine or an aging potion, ignore age as a factor. I urge you to simply focus on being a good leader.
Question Number #2:
You are asking a good question that many people have asked before. My favorite view of this issue can be Googled as “forming, storming, norming, performing”. You will find many articles to read on the concept.
One page that I liked best for it simplistic overview was at http://www.mindtools.com/pages/article/newLDR_86.htm
In a perfect world, as a leader you should be able to organize and drive your team all the way to maximum performance. In the real world, the only person you control is yourself. Sometimes team members are just not capable of doing their part in terms of performance and/or being able to get along with the other team members.
The “forming, storming, norming, performing” concept recognizes that a team will go through different stages. There are no simple answers on how or when the different stages are reached. I do think in regards to your question the concept guides when to remove people from the team. If you have one and only one team member who is preventing the team from hitting the performing stage then they should be removed.
(I stress only one, because if multiple team members are involved it is usually still a norming or leadership issue. This is not a hard rule though. Examples: If one person pisses off everybody at least once a week, he should be booted. If two or more people have disagreements about an issue, the leader should mediate and/or make the final decision.)