I think that I was in my early teens when I started reading "grown up " books. I couldn't definitively say which was the first, but I do remember becoming a wee bit obsessed with science fiction and with horror. Typical teenager? H.G. Wells The Time Machine, The War of the Worlds, John Wyndham The Day of the Triffids, The Midwich Cuckoos, The Kraken Awakes, Trouble with Lichen. Also enjoyed Dennis Wheatley and Bram Stoker. If I was a teenager today I suspect that I'd be a Goth. DH and I actually attended the Goth Festival in Whitby about 5 years ago, suitably attired, as a one-off bucket list treat. Had a great time and met some lovely people.