Both the above answers are wrong since the introduction of the Licensing Act on 24th November 2005. You can be in the bar of a hotel, unaccompanied by an adult if you are 16 or over at any time. Under 16 you must be accompanied by an adult of 18 or over. Between midnight and 5am, no one under the age of 16 can be present even if accompanied. There are some premiseds which have a ban on under 18's which have carried over from the old legislation. Some impose an age limit on themselves.