Complain about work: check and check. This one just came naturally to me. By this age, most people are just getting into this. I've been going strong for years.
Complain about aching joints/back. I just started to get into this, but I now vow to put more effort into it. The little I have dabbled in this, it's been fun. It's a good outlet, and as an added bonus, it's very annoying to those around you when you do it. I don't see any downside to this. With any luck, I can throw my back out, and then no one will hear the end of it. I'm pretty excited about the idea.
Act mature and grown up. Check, check, and triple check. I mean, people have been complimenting me on my maturity, adulthood, prime of life, ripeness, mellowness and development for years (Sometimes using the synonym feature in Word gives you interesting results...). When you look up maturity on wikipedia, it just shows my picture (provided you look within the next 10 seconds before it gets changed back to a less true definition).
Clear cut and to the point, you can always trust wikipedia. Just like you can always trust everything said on this blog (with possible exception to things said in the comments).
Reminisce about the good ol' days. I don't know if this task actually falls into the responsibilities of my age group, but I'm willing to take it up just in case. Man, things were good back then. So much better than now. And have I told you how much better the cartoons were when I was young?
Yup, that's right, I'd definitely say I earned this.