It`s best to have your perimeter ending just below the occipital bone rather than actually on it.
As you are that bit older, I guess you need a density which is age-appropriate and allows for a nice degree of scalp show-through. You see older guys who have naturally thick, relatively full, heads of hair albeit quite grey /white, but usually older men have thinner hair even if most of the head is actually almost fully covered [ not receded much].
I`d suggest you try similar to what I`m wearing.....55% top and sides and 60% on the back....I was thinking /wondering would 50% on top be a little too thin ? If you get a 55% top and you feel it could do with being a little less dense, it can easily be thinned a bit using a hair-removal cream dabbed on carefully to the knots here and there...at least you`d have that option, whereas if you order it too thin, you can`t add hair in, so I feel that`s probably what will work for you--you can always tweak it a bit on a subsequent order...the first order is always a bit daunting until you actually see the finished item in your hand and plank it onto your head to see what the `new`you looks like ! You could ask for a little `extra`graduation at the front [systems are graduated as standard]..that will mean the density will be that bit thinner for the first inch or so thus adding to the realistic visual effect to the casual observer. Hope that helps...regards, Paul.