Simple -- it would give away my age to the under-25 year-old sugar babies.
Source: "Teens Don't Tweet" (Nielsen Wire).
I recall not long ago when one of my undergrad chick friends left a Facebook status update saying, "what is this twitter all about? i don't get it." All of her friends left similar responses about how pointless it is -- and one may have even mentioned that it was for old people, although I could be imagining that part. Of course, Twitter's pointlessness was not the reason they weren't into it -- hell, they post pointless status updates on Facebook several times a day. But they sensed somehow that it wasn't cool young people doing it, but rather the "mom from Mean Girls" crowd. Young people's social antennae are hyper-sensitive, so don't try to put anything past them.