Most Facebook users are older, 35-54 now largest age group
sfgate.com
sfgate.com
More 35-44s than 25-34s would be news.
And my cubemate is Facebook-friends with her manager, which makes for an interesting dynamic in what she can or can't post online...
The 30-40 age group might actually be beneficial for Facebook. This group arguably has highest disposable income. I would think this age group is most likely to spend money on Facebook apps.
By making sure everyone's 'view' is different, they fight this a little. Facebook to a college student looks dominated by students and student-related activities -- even if dad and granddad are just a few links away.
They may eventually want to offer a differently-branded sub-network, though, to combat the risk from a youth-oriented competitor. Use much the same backend, but dress it up so differently you know the old folks and professionals won't show up -- and your activity in one sphere is clearly distinct from the other.
The problem is that is Mum checks facebook once a week, 19 year old daughter doesn't want to post drunk pictures of herself making stupid sexy faces at last night's party.
On the other side, as soon as you accept a friend invite from your mom, your privacy is gone. Sexy pics, quizzes, 5 favorite beers, etc. Most people don't want their parents seeing that stuff.