I think 13 is young enough, if you want to go earlier go for 12 or so. Then again much younger kids are already hanging out on internet.
What they really want Facebook to be is to be some sort of identity skin.
In the not too distant future you can post the first echo scan on your own facebook page. They will create a new page for your baby and also predict your babies name with an astoneshing success rate.
That of course is progress.