Roger Moore in Live And Let Die. He was 45.
If you count David Niven as 'Sir James Bond' in
Casino Royal -1967 then it would be him.
He was born in 1910 which would make him 57 years
at the time.
Sean Connery -- Aug 25 1930
31 when he was hired for Dr. No (Jan 16 - Mar 30 1962)
36-37 when he quit after You Only Live Twice (Jul 4 1966 - Feb 1967)
40-41 when he came back for Diamonds Are Forever (Apr 5 - Sep 7 1971)
52 when he came back for Never Say Never Again (Sep 27 1982 - 1983)
George Lazenby -- Sep 5 1939
29 when he was hired for On Her Majesty's Secret Service (Oct 21 1968 -
Jun 23 1969)
Roger Moore -- Oct 14 1927
45 when he was hired for Live and Let Die (Oct 13 1972 - Mar 15 1973)
56-57 when he quit after A View to a Kill (Aug 3 1984 - Jan 16 1985)
Timothy Dalton -- Mar 21 1944
42 when he was hired for The Living Daylights (Sep 29 1986 - Feb 13
1987)
44 when he made his last film Licence to Kill (Jul 19 - Nov 18 1988)
Pierce Brosnan -- May 16 1953
41-42 when he was hired for Goldeneye (Jan 16 - Jun 6 1995)
48-49 when he made his last film Die Another Day (Jan 14 - Jul 2002)
Daniel Craig -- Mar 2 1968
37-38 when he was hired for Casino Royale (Jan 30 - Jul 21 2006)
http://article.gmane.org/gmane.music.dadl.ot/33430/