I'm 20 years old, and this is a pretty comprehensive list of all the horror movies I've seen thus far in my life. It ranges from crappy 2000's horror movies and remakes to genuine classics. Some I'd really recommend if you've never seen:
Crazy, crazy movies: Suspiria (both the 1977 and 2018 versions), Hereditary, Midsommar, The VVitch, The Lighthouse, The Neon Demon, Mother!, American Mary
Classics: The Shining, Halloween (1978), The Wicker Man, Psycho, Dracula 1931, Scream, The Silence of the Lambs, The Texas Chainsaw Massacre
Creepy, ghosty: The Woman in Black, The Conjuring, Sinister, It Follows, and the first and third Paranormal Activities (which are alright and fun)
Others: The Babadook, Let the Right One In, 28 Days Later, Cabin in the Woods (so fun, esp if you've seen Evil Dead), Train to Busan, Pan's Labyrinth, and Trick 'r' Treat; I also LOVE the Final Destination movies even though they aren't that great, and Jeepers Creepers is fun too!