DS1 has shoulder length hair. Generally just about the length so he doesn't have to tie it back which he takes issue with due to sensory issues.
Longer works well for him as his hair is thick with multiple crowns and a cows lick. It has a very strong split so doesn't take a fringe, and he had a very large and knobbly head in infancy so too short would not have suited him at all. It probably is better now, but it still isn't a great shape for very short hair. Long hair weighs it down in one direction and hides his head shape.
It's a short-hair school/ area, and the good thing is that I can pick out DS1 & DS2 from across a park because of the movement of their hair
(DS2 is a bit shorter, long enough for curl and being a bit shaggy. He has finer hair (compared to DS1) and it suits him well)
He does get mistaken for a girl, but he always did even as a bald baby. I think it's his thick, long eyelashes, and has a slight, lean build. He refuses to wear trousers due to sensory issues so always has the knobbly knee look. He loves soft fluffy clothes and does get "girls" jumpers, usually mainly neutral with a pink zip. He's happy with his look and perfectly old enough to argue about it!
My only gripe with long hair is when it's overly long and stringy because it's too long for the lack of thickness. Very young girls tend to be prone to this. A bit more patience and trimming the ends makes a big difference.