Playing early 50s is perfectly possible for someone in his 40s. 

The children in the book saw him as a very old man - try asking a 9 year old how they see the eldest teachers at their school, or their neighbours who are only 50!

Okay, I have been watching All Creatures Great and Small on PBS and I feel like Samuel West, who plays Siegfried Farnon could be a good option for Professor Kirke. He's currently 54, with a younger face, and has an interesting attitude in the show; where he is in a mentor position.

Also, Nicholas Ralph, who plays James Herriot, could be an excellent King Frank. It doesn't help that his character is in love with a character named Helen.

Posted by: @lu_valient

I feel like Samuel West, who plays Siegfried Farnon could be a good option for Professor Kirke.

Just curious if you remember he played Caspian in BBC's Voyage of the Dawn Treader? It'd be fun to have him return to Narnia, but I don't think I'd want him in a big role. 

@fantasia wow, I totally forgot! Now you mention it though, I see him as a child in my head. It could be interesting to see him play the professor; as he had a fairly comparable experience to young Diggory.