I love long hair on guys. My boyfriend's hair goes down to around the small of his back so obviously I really really like it :) This guy's hair is pretty much perfect (also quite similar to my boyfriend's):
Short hair is fine too, but I just have a thing for long hair.
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I don't care.
I would advise guys under 20 who don't have especially hard/mature features to not have long hair. It can be inherently feminine. If you look like a viking its badass. If you look like most teenage boys, it makes you look like an ugly girl.
Be careful about reading into 'girls like guys with long hair', since they're typically thinking about square jawed muscular guys,
I mostly like short hair on guys, but I have seen guys rock having long hair too... so I am not against it. The length you posted isn't bad and can be hot on a lot of guys. Flowing long hair might be bit harder to get into but it's not a dealbreaker or anything. I can learn to dig it if I like the guy.
I don't think all guys should base what they do with their body on my opinion or anyone elses. I strongly prefer short hair, but I don't discourage guys from growing theirs out. It isn't about what I like.