i havnt read this whole thread, so apologies if anyone else has pointed this out, but from what im reading i dont expect so.
fat around your middle is healthy, especially in middle age, studies have shown that people who carry a reasonable amount of fat can better cope with stress and illness, it has even been shown to prolong life by a number of years.
it seems likely to me that the paleo-diet is working very well for you, fat storage is a natural function and you body is simply saving a wee bit of energy against a rainy day of no food or sickness where you cant eat.
a few years ago i caught the dreaded swine flu(probably, i didnt seek medical help so we will never really know) for 3 days i lay in bed coughing continuously, and i do mean continuously, every second breath at best, i saw red, white, grey, yellow and green phlegm, i didnt eat, i did manage to drink water, but it was extremely painful to do so and trips to relieve myself and replenish my water were harrowing, nobody looked after me and i couldnt prepare any food, i did towards the end manage a bowl of 2min noodles with some frozen vegies, by the time i emerged i had lost most of my muscle and all of my fat, i actually got comments that i looked good from female friends, haha(im not overweight but i have a paunch).
i think if i had been skinny i would not have survived that ordeal without constant nursing.
so i consider that proof that fat is actually healthy, -having said that id love to have a flat stomach again .. sigh
what are your reasons for concern about gaining fat?
if its simply health i suggest you forget it, if its vanity... as you were.