Worth discussing is how long Mark has been eating his current diet. The skin is substantially less susceptible to burn when you get more Omega-3 and less Omega-6 (a relatively simple switch led to a 2x time to burn in a hairless mouse skin cancer model). Mark obviously hasn't always had his same diet, re: his days of competitive marathoning and demolishing half gallons of ice cream.
I do think that's one of the more unflattering pictures of Mark I've seen. The other thing to take into account is that that picture is of him at 50, and he's 55 now. If you go compare with a picture here: http://www.marksdailyapple.com/about-2/mark-sisson/ it looks more like he's gone from 50 to 45 in terms of how his skin looks in the last 5 years. Maybe Mark can enlighten us about what his diet had evolved to by that point in time.