When the 007 franchise launched in 1962, Sean Connery was 32 when he received his license to kill. That was almost 50-years ago, and James Bond has aged like a fine Beaujolais spiked with antifreeze. How is the same 30-something special agent who fought the Cold War-era Russians now taking on post-9/11 terrorism?
There has been a theory among fans that there is no one single James Bond, but that "James Bond" is a codename passed on from one agent to the next as each retires (just as the titles of M and Q pinball from agent to agent). The theory explains the agelessness of Bond--note that Daniel Craig's Bond became 11 years younger whereas Judi Dench's M aged by four years.
This also explains how James Bond's personality changes dramatically from actor to actor. For example, in one film you have Timothy Dalton's Bond burning a man alive (around the 9:00 mark). Pop in another DVD and you see Roger Moore's Bond is doddering around in a clown costume.