You have to be careful with what you look for with a relationship with an older woman. 20+ years difference is possible, but it takes a big deal of giving. Ask her out to some coffee with the excuse of discussing about class. When you meet her, smile a lot and give her some hints by touching her arms or hands. Then you can just tell her she's sexy and you want to meet her in some other occasion to do something.
In Dating an older woman thread, http://4-ch.net/love/kareha.pl/1158778452 Serverin approached his date and it went well. I wish you luck also.