I don't think it's the age or age difference, I don't think it's you being too needy.
I do think it's normal for him to be this way, and that the "go-getter"-ness in work and his inability to pay attention to his personal life, not to mention the quick speed at which he likes to "move in" and get you working with him, is all probably a big part of what led to FOUR divorces by the age of 43.
That's scary and you would probably do very well to not try and be "the one who changes him."
Just because "he's ready to take the next step with you" does not obligate you to be in step with him at this point when he "forgets to call you," doesn't prioritize your contact or leaves you hanging for entire weekends without explanation.
It has nothing to do with age or being divorced 4 times, it's the way he is so it's normal for him.
Why are you settling for someone who doesn't meet your needs? Most people have some good qualities, but it doesn't mean you should be in a relationship with them if on a daily basis you are unsatisfied, frustrated or upset.
Look for someone who makes time for you, and treats you the way that you would treat him.