A colleague in my last job noted that since I have a "baby face" I should always wear my hair in a short "professional" cut, so  I don't look even younger. At the time, I thought to myself, "It's ok to look younger-I'll be glad for it when I'm older." Still, I do wonder...where do people get these ideas?
Anyone else come across weird perceptions of age appropriate hair making you look older or younger?

I've never understood the "short is more professional" concept.  I personally think a french roll, or a bun is very sophisticated looking.  Long and loose may not be the most professional, depending on your job.  Hair getting caught on chairs, desks, in food, etc., is never appealing, but it can be done.  I like the front pulled back and off the face, and the hair loose down the back.  If the hair is in good condition, this can also look business-like. 

How you dress and act is a much more important factor for professionalism.  I've worked with men with hair to their waist in a nice, neat pony tail or braid and tats down the arm, who were very professional.  I've also worked with men in the traditional suit, short cut hair, that were inconsiderate slobs.  Me.... I'll take the long haired professional.    The same is true for women, of course. 

I've often heard the "too old for long hair" concept, which is absolute crap, but I've never heard of the length of anyone's hair making them appear older or younger. Amazing how influential one person's opinion can be on another's psyche.

As for "professionalism," it depends entirely upon said profession. If you work in the food industry, keeping your hair out of the way is essential. But in a corporate environment, anything goes. Pretty much any style is accepted as long as it's not neon green or pink or whatever. 

When I was in my early to mid twenties I used to try to look older, but now that I look back on it, I don't think it helped me.

Maybe it's because I'm pushing 40 now, but I see absolutely no professional advantage to looking older, and I think this applies even to a woman in her twenties.

This is my opinion (and I acknowledge I am making broad generalizations here, and this does not always apply to everyone or to every workplace culture):  Whereas an older "distinguished" look can be helpful to a man in his career, an older look does not help a woman, so I would have to vehemently disagree with that former coworker.  Of course, one does not want to try to look too young, but I don't believe there is any sense in a woman trying to look older.  But in my case I am a female professional working in a very male dominated field, and it's always been that way for me.  Maybe it's different for different circumstances.

Now, as far as hair and age perception, I think that there are ways to wear your hair that will make you look older or younger whether it's long or short, but that length of hair does not make any difference.  It is relatively common for female executives in my large company to have longer than average (but well maintained) hair, and in my biased judgement long hair actually puts a woman at an advantage, at least from my experience.

So I say keep it long if you want, and I believe there's a good chance she was jealous.