First off, Connery was 31 when he made Dr. No and 40 when he made Diamonds.

That said, it's difficult to keep any actor over 40 when the films are spaced out by 3 - 5 years.

that the first 5 Bond films were released in a span of roughly 4.5 years.

Perhaps would be best to speed up the production a tad and stop trying to make each one bigger than the last.