I have this argument with my parents all the time.
I can even point to their own young adult and current photos.
Yet they insist “I never heard that. I’ve heard your ears get bigger, but not your head.”
Apparently pictures are not enough.
Any data on this?
I think there would have to be more information on this, like the time scale over which this change has taken. For instance, Paget’s Disease, a bone disease seen in older people can present as increasing hat size.
No data, but look at pictures of Frank Sinatra’s head when he was young and when he was old.
Barry Bonds seems to support this theory.
I’ve wondered about this since my Borsolina no longer fits.
Yeah but he got wider all over, didn’t he. There is fat in the face, which will give the appearance of a bigger head if you increase in all over weight.
And, not to bring up a sore subject, but isn’t he one of the steroid users? I’m not sure we should use someone who’s dickered in growth hormones as our test subject for normal physical development.
Yeah, I admit I was being flippant. By some estimates, Bonds’ head increased by 1-1/2 to 2 hat sizes. But not, as you note, as the natural product of aging.
ETA: His head didn’t grow that much, but apparently HGH can cause growth in the skull, as well as the hands and feet, all of which Bonds has apparently experienced.
Ah. That explains the whooshing sound over Chicago just now! 
For the most part the skull itself doesn’t get bigger once the individual is mature.
However deposition of subcutaneous fat will certainly widen the overall head, and an increase in the musculature would do the same thing.
Some conditions will change the shape and size of the bone itself, but I wouldn’t consider this to be “normal” (i.e. non-pathologic).
I was recently talking to my aunt about fancy synagogue hats, and she commented that she always keeps hers, because they’ll come back into style in thirty or forty years. She’s in her early seventies, and wears hats she bought fifty years ago, implying that her head, at least, hasn’t changed much.
They do in Innsmouth…
It depends on how successful they are in life.
I certainly hope not, I have a devil of a time finding hats now as it is.