Hi,
I would be fine, if any of my sons were the same age, leaving them alone around the Hotel so long as they were trustworthy. Where is you hotel?
In the centre of Salou alot of the locals hang around by the beach playing footie, and also morrocan lads and are usually not a problem, i have been loads of times and have only heard of/seen fighting going on between them once but had nothing to do with holiday makers.
I would maybe let him go a bit further if he met some other sensible teenagers, safety in numbers
I hope you have a good time,
Loulou