My tastes have evolved over the years so that I've always been especially attracted to women in my own general age range. That's the way it is in real life, and that's the way it is with celebs.
These two are probably at the very top of my list (and they are both very near my actual age):
I was crushin' hard on Ms. Lane when I was 14, and I'm still crushin' hard on her as we both approach "half a hunnerd" in the not all that distant future. As for Ms. Parker, she's the epitome of cute for me. Doesn't hurt that they're both really good actresses, either.