Unfortunately lots of Yr 8-11 are watching it! It's the talk of all the secondary schools round here. My DD watches it (Yr9, age 14) as do all her friends. She watched last year (13) without my permission nor me knowing, on catchup & at friends houses initially. DCs' pesky 'computer&smartphone' generation are far more adept at getting round parental IT blocks, than I am now! It's easier to restrict this type of thing when they are under 11/12. As with all things it get harder and more about talking, negotiating and bringing up your DC to think for themselves as they become more independent teenagers.
My DD and her friends watch it for a variety of reasons, (a study in ..) friendship/ relationships, fame, gossip, silly behaviour, bikini fashion and make up advice (!!). DD and her friends definitely don't agree with some of their behaviours and DD says she tends to skip the yukkier parts ( you really can't see what they are doing if anything a bit sexual btw), although really she hears more from older kids at school who could tell any story!! Fgs she's reading Romeo and Juliet at school where the teenage romantic leads commit suicide! ( I remember by her age having read Lady Chatterley's lover, Joseph Conrad's Heart of darkness, Lord of the Flies.. all with very adult themes! This seems mild compared to that and not worth the judgy pants some PP have put on, although parents must make decisions for their own DC.
We talk if there is something a bit dodgy on Love Island but usually after each episode she volunteers it to me about 'who was an idiot' and 'what she would have done'. She's also full of views to share on when someone deals with something well or shows themselves to have a nice character. I've overheard her convos with friends about it as well and feel they are all very sensible. I don't think these contestants are their idols!
To me it's a show with a microcosm of human egos & behaviours and some banality, just what teenagers love & use for debate. And DD said I've shown her worse on TV as I 'made her' watch Bridget Jones Diary with me (tis true, she was 14) and she said they have sex in there - to which I replied "Yes with Hugh Grant though... entirely different!" 
DD also thought Bridget Jones Baby was dodgy too as Bridget couldn't work out who was baby's father after unprotected sex with two men within a week (although it was nice how she dealt with it)... I don't think DD's morality is being warped at all by L.I. as she clearly can separate herself from what she watches.