When I was in law school, it was my experience that us older-types in general had an advantage against people who went to graduate school straight out of undergrad. We had more real world experiences, and with that a stronger sense of the advantages of having an advanced degree then those who hadn't worked for 5-10 years. We had less of an interest in partying four nights a week and consequently more time to study.
There were disadvantages too. I really couldn't stay up all night studying the night before a big exam. Consequently, I had to plan my time better leading up to exams and assignments.
I'm not sure that getting a PhD at my age, 36, is worthwhile, but I figured I'd give it a shot and see if I could get in. It's really up to everyone to make that choice for themselves, but if someone told me they thought it would be a good idea for them, I'd say go for it no matter what their age is! Nobody knows how long we have to live. I've known professors who worked into their 80s and 90s, so being 42 and starting an academic career doesn't seem that bizarre if I have another 40 working years after it.