Last time I had mine cut I was in the middle of the awkward phase a little behind where I am now, if I hadn't cut it then I would have pretty long hair by now. I felt pretty shit when I realised I still wanted long hair so I don't think I'll cut it again.
I agree that it looks smarter tied back, and it does look a little messy at the back, but in a few months I'll be able to tie it back anyway... besides they let sikh men wear a massive turban, carry a knife and wear a huge beard and muslim women to wear headscarfs and loads of baggy clothing (and sometimes a beard too) so I'll just kick off if they say I can't have long hair.
Luckily because I am in the UK and will be working for the NHS they are generally pretty liberal about these sorts of things. We have only agreed to "look respectable" and there are no hard and fast rules so provided I keep my hair tidy I should be OK.