I remember reading that Dalton was in his twenties when offered the part, but he decided he was too young to play James Bond, so turned it down.
Interestingly, Roger Moore was an initial candidate for Bond, but couldn't be got due to TV commitments, so Connery got the gig. Dalton was wanted, but turned it down, so Moore then got the role. After Moore, they wanted Brosnan for the role, but again, TV commitments kept him out, so the role went to Dalton. Then Brosnan got it when Dalton gave up.
I always thought this was a funny pattern. Its a shame they didn't want Daniel Craig to take over from Timothy Dalton, just to keep the pattern alive!