I know what's making me hesitate: In my culture it's generally considered rude to ask someone older than you what their age is. (And the larger the age difference, the ruder it is.)
Cultural factors are important. I would just challenge you a little to consider that some people who are older than you might not like this cultural tradition. I don't know if there is a polite way to find out, but I personally don't feel like an older person. Even my Mom doesn't feel like an older person! Being treated like an older person when you still have that same young enthusiastic person inside of you can feel like you are being excluded for nothing more than how you look.
