I'm 27, and I'll be 28 when I begin this fall, in a PT program. I have five great years of work experience that I expect will help set me apart from people who came immediately out of college. I know there are rumors of Biglaw being biased against us "older" students. It may be true, and it may not be. If I were a hiring partner, I'd want an associate who has some professional experience and has been through contentious meetings, intraoffice conflicts, etc.
I went to an admitted students open house last weekend. I definitely noticed a bunch of younger students (there were older ones too, but I couldn't tell if they were students or parents.) So is 28 old for law school? Maybe. Too old? No.