For an older iron fist I think that Jason David frank would be a great older Danny rand. This would be great for a number of reasons. Maybe 3. But again this is just my opinion. So is you don't like it then your in luck because I'm not an important person in marvel.
1. He is a great martial artist!
Iron fist is one of the greatest martial artist in the marvel universe. So for an actor they need some one who can do that, and is also a good actor. He is also been power ranger's tommy Oliver. There he shows that he is a great fighter and in newer seasons a great actor.
2. An established super hero would be great for the Netflix shows!
With the other Netflix heroes being newer people it would be good having someone who has been doing this for a while. In the daredevil series he recently started and Jessica jones has been around with her powers but has not done heroic stuff until the series. If he would be cast it would mean he would have had experience doing this and a great leader for the other heroes.
3. Jason David Frank is a great guy!
Marvel has cast a lot of good people in there movies so kids and fans would would like them better. Also his popularity he has gotten from the power rangers would bring a lot of new people to watch it to see how he is like outside of power rangers.