If long hair is a sign of Noxian aristocracy then why does Draven have long hair?

Because Draven doesn’t care about what other people think unless they think he’s awesome for how eccentric he is.

The reason you see nobles with long hair is that they like to showcase their cleanliness and properness. When someone has long hair, if it isn't cared for properly, it's a hot mess. It's tangled, greasy, and could be frizzy and all over the place. Most commoners would have a tendency to not care for their hair as meticulously as a noble, which is why nobles would favor the style, as it's just another way to showcase how much better they are because they can put effort into their hair.

Its not like there are people running around the streets of noxus cutting the hairs of the commoners,just to ensure that they don't have long hair.

Aristocrats tend to have long hair because they think it is fancy,that doesn't mean that commoners can't grow their hair long as well.

Because that idea was created to justify Swain's long hair, not the other way around. LeBlanc doesn't have especially long hair.

Draven is Draven thats my explanation

Well... Draven is famous.

Swain is a usurper, tyrant, murderer, rapist, pillager.

All hail Boram Darkwill

You're taking it too literal. Not that serious

Obviously he really wants to be fancy. Trying a bit too hard.