I wonder how many of you that say he should have made SURE she was not lying about her age, have asked to see identification of every guy you've slept with.
Again, I think the important point is that when you choose to have sex with a drunk random you pick up at a taxi rank you are leaving yourself open to all sorts of risks. The person may be underage, or have an STI, or be married, or be a serial killer.
I'm not suggesting that there is a possible mechanism for checking for e.g. age, but that if you engage in casual sex you should be aware of and accept these risks. This individual raped the girl, not because she looked older, or was out at 4am, but because he didn't know her. He could just have well caught say herpes, which he would also have to deal with. In the event it was rape, which he should also have to deal with.
If you choose to have sex with an unknown, you shouldn't be able to use the unknown aspect as a mitigating factor, as you know there are many unknowns.