It's essentially a business degree with classes in database, programming (more geared toward business applications, database integration, etc.), and networking. In the MISM (the Masters for IS), the classes become more focused (fraud detection, additional programming, web development, etc.) depending on what niche you want to go into. I have not done the MISM (only one more year after BS), but have considered it. It includes some MBA classes as well.

As far as it being referred to as "ISYS", that was just the prefix for the classes at BYU (to answer one poster's 'never heard it called ISYS' point). As far as in the industry, I have mostly heard CIS or MIS, but they are all essentially the same thing.

As another poster mentioned, CS is much much more heavy on math and logic and how it applies to computer programming. If you want to do software development, you can probably do either (CS is probably a better degree for that), but if you want to do business analysis, consulting, management, etc. I would say the ISYS/CIS/MIS degree is a good way to go.

As far as picking it up, I don't think age has anything to do with it, as long as the interest is there.

Good luck!