Interesting take on it - cut his hair because some kids have been brought up thinking it's ok to bully other kids when their hairstyle doesn't fit a stereotype? Yeah, no. I'd rather encourage my son to keep his hair as long as he wants for as long as he wants.
Sadly some kids always bully, and a boy having a very feminine hairstyle is more likely to become a target.
It’s not about a haircut sending the right or wrong messages, more the damage bullying or prolonged teasing can do to a child’s self esteem. If he’s very confident, assertive and sure of himself then peers’ opinions won’t matter to him and he can shake off any negative comments.
Has he grown it long because he genuinely loves it this way... or is he trying to please you, knowing you approve of his non stereotypical long hair?
You say you’d cut it if he asked, but contradict this by saying if he wanted it cut due to bullying you’d encourage him not to. Yet wanting to fit in and have the respect of peers becomes very important to most kids at some stage. What’s wrong with wanting to blend in and have a hairstyle like the boys in his class, if that’s what he wants at some stage?
There are so many lovely short hairstyles, I find it hard to understand why you consider all short hairstyles ‘stereotypical’?
Personally I wouldn’t let my DD do something drastically different with her hair at this age, as I feel it’s setting her up for being teased or bullied. At 6 I’d rather she valued other things over her hair, so we keep it in a practical no-fuss style that suits her and is easy to care for without clips or bobbles or grips. When she’s a teenager she has plenty of time to experiment with her hair and challenge social norms (if she wants to).