I don't think it would ever necessarily be inappropriate unless you wore it to mass or a funeral or something like that. (It would depend on how conservative your church/temple/friends/family are.) Paired with the right clothing anyone can wear a smoky eye, I think - *how smoky* would be the variable though.
I totally agree with islandqt in that the condition of your eye area and the shape of your eyes has everything to do with pulling off the look. For example my mother is in her 50s and I would never recommend a smoky eye to her - not that she's extremely wrinkly (she's beautiful!) but her eyes are deep set and with her crow's feet, her eyes would get lost in dark shadow. My eyes are similarly deep set and I highly doubt I will be able to wear dark shadow when I'm her age either. My mom has hazel eyes and medium-light skin (she's way more tan than I am), and she loves Urban Decay 24/7 Glide-On Eye Pencil in Stash and Gunmetal, and Smashbox Eye Illusion shadow quad (she uses it every day).
I think Jane Krasinski's eye makeup on 30 Rock (her character is Jenna Maroney) is beautiful and mature. They always have her wear very brightening silvery-pinks and the result is gorgeous. She's not in her 50s but I hope you see my point about makeup on mature women - you can do whatever you want but most women just go with what looks the very best as they age.
You probably don't want advice from a 22 year old on the matter though!