As I'm 41 years old, I still find Amy Adams to be quite "hot" in spite of her advanced age. 

I thought Amy Adams was a good choice. I just wished they had dyed her hair darker.

I get what you're saying, but you have to consider that these actors only have a 2-3 film life in a role to begin with (the Harry Potter films notwithstanding).  If you film the first film in 2015, release it in 2016, then film the next one in 2017 and so on, that is 6-8 years of an actor's life in one role, and most are not going to want to do the same thing forever.  In the instance of Marvel films, they don't go on a two-year cycle, so you are looking at 3 years per film, and that is almost a decade as one character, at which point they will have outgrown the role and moved on to other things. 

So you either reboot entirely or do what will happen with the Marvel movies, where they simply farm certain characters out.  RDJ is not going to be playing Tony Stark five years from now more than likely, because Marvel is not going to be including TS in their movies; they'll go with War Machine or some other person in the suit, but RDJ isn't going to be that guy.

There's another option. There are very few roles so uniquely identified with a single actor that they must be retired rather than recast (Lt. Columbo comes to mind). How many Bonds, Poirots, Holmes' and Charlie Chans have we had? Even Hannibal Lecter has been successfully recast with the delicious Mads Mikkelsen assuming the role from Anthony Hopkins (a role I would have bet money belonged to Hopkins alone*).

With a good story, a quality production and strong actors, audiences can be very forgiving of a new face in a familiar role.

(*And yes, I remember that Hopkins followed the great Brian Cox as Lecter.)

Man of Steel took place at the beginning of his career though (IIRC) so a young Superman is reasonable. I liked the film and thought Cavill was very good (and really, didn't seem that young, esp. compared to Routh.)

Maybe. I think avoiding the issue in the first place is what I'm getting at. Just don't put yourself in that position. I don't see what the problem is in getting someone of a certain age to play a person of a certain age. Granted in the case of Lois, it's never specified in the comics what age she is or isn't, but I've always guessed mid twenties to early thirties at most. Just the way I would do it, if I'm kicking off a franchise, let's see a new Superman franchise, if I have two actresses where both of them can nail the role except one is 30 and the other one is 40...why wouldn't I go with the one that is 30? Assuming she is just as good and has chemistry with the cast.

Yes there certainly are youthful people who have talent and ability. That is not the issue here. If your criteria for evaluating performers or people in general is their age or how they look, and dismiss people who don't fit your criteria on those issues, then acting ability (or ability in any field) isn't figuring into it. If you are evaluating on acting ability (or competence in other fields if we move beyond acting), then whether they look good and how old they are are non-issues and not relevant to the conversation. If your first question is Are they hot? or How old are they? or if those are what you evaluate performers on, then you give the impression their ability to act and deliver a quality performance does not matter to you. If they can act well and deliver a quality performance then age and hotness are irrelevant, and dismissing Amy Adams performance as Lois Lane because she should have been hotter or younger is a prime example of that. So yes, young people can act, I never said they couldn't, but the cult of youth and appearance doesn't ask can they act, they ask are they hot and how old are they...and if that is all that matters to them, then they shouldn't be surprised when they don't get quality out. Output comes from input, if you don't consider the quality of what you put into a project, you shouldn't be surprised you don't get quality out of it. 

I've seen the quote attributed to both Oscar Wilde and George Bernard Shaw, but there is a certain truth to the idea that youth is wasted on the young, and if I only knew then what I know now. When I was in my twenties I would have told you the ideas in those quotes were full of sh*t, but I've come to realize I was full of sh*t when I was in my twenties too, and it got worse before it got better. Of course, ten years from now I will likely look back and realize I am still full of sh*t now. 

-M