You're right about that, Dr. No. Even in his late fifties, Roger Moore still looked younger than Craig does in his early forties. From Quantum Of Solace to Skyfall, Craig looks like he's aged about ten years. I can't understand why they would want him to play Bond for who knows how long, because even though he's physically fit, he isn't aging very well facially.
But the Craig fans will just say that Craig's physical build is a good enough reason for him to keep playing Bond for eternity, and that his ruggedness gives him the appearance of an experienced/cold-blooded agent. I've even seen a comment from a person at IMDb suggesting the use of CGI to make Craig look younger if it was absolutely necessary, and this was right after they were bashing Roger Moore for being too old in A View To A Kill.
Pierce Brosnan at the age of 49 in Die Another Day equals: "Meh. Too old."
Sean Connery at the age of 52 in Never Say Never Again Equals: "Sean, you were great during the 1960's, but... uhh...."
Roger Moore at the age of 57 in A View to A Kill equals: "BLASPHEME!!"
Daniel Craig plays Bond until he's an old fossil equals: "Wow! This is the greatest thing ever!"