Same happened to me as I got older. I once was kinda skinny but as I aged I got fatter. Not fat as in 300lb huge, but my neck and face got more blubber and I got a beer belly now. I think this is rather common for two reasons: #1 I have a bigger appetite today than I did when I was younger and #2 I drink alcohol routinely (not every single night but pretty much every other night). The combination of getting older, eating and drinking more often can fatten you up over time. Ever notice why in high school the nerds were always skinny and the jocks who liked to party all the time tended to be on the heavier side? Same reasoning.