Welcome to GreekChat!
At 19, you certainly wouldn't be too old to rush - at most schools. Your very best bet is to read the hundreds of threads under Rush, and see if any of the threads even mention the school in which you're interested.
Obviously, each school is different. The rules (both the rules of the school, and the unwritten rules of those who have been through rush at the school) will range from incredibly strict to downright casual. That said, it is NOT always to your advantage to say which school you're going to attend on a message board, as many of the various sororities read the posts, and may make a quick decision based on one poor post. Again, as you read the Rush Forum, you'll notice that most Potential New Members will use nicknames for the different GreekLetterOrganizations, just to maintain some privacy.
As for being foreign, many chapters would consider that an asset! Love those British accents!
For the most part, the people of GreekChat are more than happy to help you through the process, though! The only stupid question is the one that's not asked. Good luck, and I do hope that you find a sorority home while here!