I'm going to agree with Amber. I don't care for being called "a female" either.
I don't mind if it's used in a scientific way. Or as an adjective. Or even if "males" and "females" are being used as the division: "Males will change in this room, Females will change in the dressing room down the hall." Or in Pea-and-Me's example "A 90-year old female..."
However, I don't like it when it's used like "Men and females" or "guys and females" and I've seen that used a lot:
Like "Are there going to be many females at this party? If not, I'm not going."
Or "The females are going shopping while us guys watch the game."
I don't even know why I don't like it... but it's kind of creepy.
If someone calls me a "45 year old female" or says "Their family consists of two males and 2 females" then there's no problem. But, "The females are in the kitchen..." bothers me.