If it's just two of you, you shouldn't encounter too many problems- me and my boyfriend stayed in a 5* (special deal on lastminute.com, their secret hotels where they have rooms empty in expensive hotels so they sell them for cheap, without giving the name of the hotel- was amazing!)
But yeah, we stayed in a 5* in Edinburgh when we were 16/17, no problems, just gave my debit card at reception where they ask for a credit card.
Then the next year we stayed in a lush hotel in Prague, again, we were worried when we had to fill in a form with all our details but it was no problem.