If you are somewhat annoyed at LJ for catering to a very young crowd and trying their best to mimic MySpace (with all the things we may not like about that site!), there's one thing you can actually do: let yourself be counted in the age demographic.
As long as LJ sees HERE that the largest number of users is in the 17-20 crowd, they'll try to cater to that audience. As long as they're looking at the hard numbers only and not at those most likely paying for the site,we might as well throw our ages into the mix.
So, if you never wanted your birthday out there, you can you to EDIT PROFILE and add your DOB to be counted in internal LJ statistics but not displayed.
Pass it on and let's see whether we can make adifference and maybe let LJ folks know that some of their most active (and paying) users are not 18 year olds!!!