is it normal to have a butt smelling fetish

So im a teenager and i like to smell girls butts but i normally do it in creative ways (shoes need to be tied, walking up stairs and ill lean in, sometimes drop a pencil). Im not proud of it but i like the smell of girls butts. I told my step sister whos around my age and she said its weird but she gets that we all have things that turn us on....but is mine normal