I'm pretty sure the only reason he shaves his head is because he can no longer grow hair on top of his head. If you look at the pic in which he's wearing glasses, you can see some slight hair growth on the sides of his head, but then the top is naturally more bald. This would be an indication of classic male-pattern baldness.

Some people do begin to lose their hair in their 20s, and at the relatively young age of 27, I'd say it's more logical than not that someone in his situation would shave his head. I mean, the alternative would be that he would let his hair grow on the sides, but then wouldn't be able to grow any on top. If you ask me, I'd say it would be even weirder for a person who's still in their 20s to be walking around with that sort of look.