Can I/Should I consider joining the PTA BEFORE my child is in school?

First off I plan on calling them, but I didn't know if you have to have a child IN school to actually join the PTA, or just live in the community. My husband and I have always said we want to be involved but our son is only 14 months old right now. We are also considering private schooling and homeschooling as well in addition to public school. Just keeping open minds and options open. But then I was thinking tonight....should we join early so we can be involved to help ensure that the schools are hearing our opinions and ideas so that the schools could possibly be more to our liking by the time our son is going there? Or is the PTA a waste of time and energy? Any feedback appreciated.