I think it's a great hobby, but also personally it depends on what kind of things you write and your writing skills. Bonus points if you write poems. :P If you write stories, depends on the genre as well. And.. maybe I'm being picky here (but I'm into reading and writing) some people say they write as a hobby but their writing isn't particularly good. It's attractive if you can write artistically. If you have a wide vocabulary, can create good metaphors, if your words flow... so to me, it's one thing to tell me you write as a hobby, but your actual writing is a completely other thing. :) The other thing I like about it, is that often writing can reveal a person's most inner thoughts and feelings, insecurities, etc. and even subconscious thoughts, especially through poems, which is interesting.
I love it , it makes me express what I'm thinking and what I come out with as I go along. But I also enjoy other things too like outdoor activities and for me it's not a turnoff. Hobbies don't define who someone is. I ️see it more as a small part of the other person and their interests.
I think it's interesting for a guy to be passionate about writing. It's kinda romantic if you think about it. I dated a guy and he wrote his own novels and they were amazing. He was a pretty great guy too. I think it's a turn on.