This is a real medical condition, and it's not really caused by sidewalks, tight socks, or age. It is an allergic reaction to solar radiation, called Polymorphous Light Eruption, or PMLE, aka "Sun poisoning."
http://www.dermnetnz.org/index.html
It is usually caused by being suddenly exposed to much more solar radiation than you are used to; which means that at WDW, folks from more northerly latitudes are the most common victims, or folks who normally spend very little time outdoors. The most commonly-known occurrence of it is among Scandinavians who go on vacation in Spain, doctors on the Costa del Sol know it very well.
Once you have it, the only way to get rid of it is to let it go away on its own. Hydrocortisone cream helps the pain and itch a bit. Taking antihistamines and using a lot of full-spectrum sunscreen before getting exposed to the sun tends to be the best prevention, other than keeping all your limbs well-covered until after sundown. Some studies have shown that using a tanning bed for awhile before travelling to the sunny place will
help "harden" the skin so that it doesn't react to the ultraviolet light.
Women apparently get it twice as often as men, and most people who are going to get it get it for the first time in their 30's. The bad news is that once it happens, the odds of it happening again go way up. I got it the first time at 36, and I got it several more times until my dermatologist had me take preventative antihistamine starting several days before going on vacation. I haven't gotten it since I started doing that; Claritin is my med of choice.
BTW: Neosporin and creams containing benzocaine will make it worse, don't try that!