Bitcoin payment is more efficient so ofcourse it can go to thw porn industry. There is no unusual in that. Bitcoins could be adopted by anyone or anywhere. Just like fiat, bitcoins should be known in every industry. 
I too consider that making payment for any subscription like digital magazine or porn content, I find some comfortable in the transactions fees involved with bitcoin compared to any other payment processors. But we need additional documents for bitcoin if age proof kind of thins are required.
Age wont really mater here in the internet. Someone could pretend to be an adult and get anything they want. You kno, internet is full of lies. You can hardly see someone who will actually be true. So the age proof for bitcoins, I don't think that'll work. Just like fiat, anyone could have an access to bicoins, unless it can be moderated by someone.