As I've grown older, the age range has widened a bit. My preference would be 21-28, although I wouldn't rule out anyone that's 20 or 30 at the most if she was interested. I have a harder time expanding the older age range though. I admit, it seems intimidating because I feel that I've barely started out in my career. And while I feel that... thanks be to God... I'm off to a good start, a woman that's 30 would probably want someone that's been tested in the world for more years than I have.
Granted... that same woman who is 30 right now would probably be within my target age range as I grow older.
At the same time... I've had to eliminate anyone under 20 if not 21 from my age range. No offense... but they just feel immature at least in the sense that they are untested in the world. Their minds are still developing and I don't know how they'll change as they become more exposed to the world. Granted... our minds area always developing... but more so in that time period. And it's hard to gauge someone's true personality when they're still living with mom and dad (for example... is she going to church only to please her parents... or because she really wants to go)?
All that said... let the age range be just a guide. Don't rule out someone right away that's interested in you, just because she's a few years older or younger.