I jus wanted to share my experience purchasing Alhambra tickets. I went through the official site and reserved my entry time. I am traveling with three adults and one youth, according to their ticketing system. The youth ticket is discounted by a few € (maybe 3€). What I didn’t see anywhere while purchasing, is that if you purchase discounted tickets you cannot print out any of the tickets from home.
I received a pdf of the transaction, but at the top of each person’s printout it says “This is not a ticket” in English. In Spanish it then says that this document needs to be exchanged for a ticket after verification of eligibility for the discount.
I had hoped to purchase tickets in advance, enter through the Justice Gate and avoid some crowds. If I had known this was not possible when purchasing a youth ticket, I would have paid the adult price. If you are considering a youth or senior ticket, please be aware of this extra step.
I have emailed the Alhambra to find out if the tickets can be printed elsewhere in town in advance, and have not heard back. I read that people have done this at the Alhambra bookstore in town.