As a long haired person who braids her hair back in the workplace (it's ranged from calf length to mid-back since I've been here) what I've noticed is that hair that is braided back translates for most people as 'short and professional' and I get either a very positive or a shocked reaction on the few occasions where I wear it loose, so there are options.

On the other hand, I work at a relatively liberal company in New York City, so your mileage may vary.

At any rate, have a very happy birthday! I don't think there's anything wrong with being the age you feel, especially since you carry it off so well.