How I know I'm getting old:
1) I remember as a kid, I used to love going down slides. LOVED it. Especially those twisty slides where you go through a long tunnel. In the last year, I've had the pleasure of going through a handful of slides with Melly on my lap, and every time when I get to the bottom, something hurts. Usually my butt. Those slides are treacherous.
2) Prior to a year or two ago, I had never experienced lower back pain. Never. When I was stooped over a patient for whatever reason, the attending would often warn me, "Be careful you don't hurt your back." I would scoff. Back pain? No, I'm way too young for that! But in the last year, I've had back pain constantly. So far, it's all just been muscle strains that got better in a couple of days, but I suspect I'm on my way to a herniated disc. I try to be careful... I tell my patients to take off their own damn socks for the EMG. I'm aware of the correct way to lift an object so as not to cause back injury, but it's hard to lift with perfect form when you're lifting a quickly moving, wriggling object, if you know what I mean.
3) I used to love roller coasters. When I attempted to ride a roller coaster a few years ago, I found that I not only did not enjoy it, but when I came home, there were actual bruises all over my poor back.
4) About a year ago, I found my first gray hair. I haven't seen any more since then, but I'm clearly still traumatized.
5) I still get the standard "gosh you look way too young to be a doctor are you sure you aren't still in grade school" response from patients, which I know most of us have experienced. The only difference is that now I'm really HAPPY when they say that to me. I don't even get fake insulted, like I used to. Then I get overzealous and injure my back while examining them.
I am impressed that people have kids after age 35. I'm not even 30 yet and as you can see, I'm already falling apart.
(Yes, I'm under 30 and complaining about feeling old... go ahead and mock me.)