Check T&C's or contact directly.
Hello and welcome to the RTA forums !
You can check out the RTA lodging link and when you have selected a hotel at the bottom you will find 'Important information' where some state anyone under a certain age must be accompanied by an adult. However I wouldn't say that if it's not stated it doesn't neccessarily mean they would be accepted. Once you have got to the booking stage you should find 'Terms and conditions' but if in any doubt contact the property directly. I believe a minimum age is 18 years but some Hotels have a 21 year old limit.