I'm not sure my issues are related to age. Something has always hurt since about age 21. I've had lower back pain, plantar fasciitis, knee pain, wrist pain, shoulder pain, hip pain, groin pulls, upper back pain, neck pain, jaw pain, finger joint pain, etc. Some issues resolve themselves after a year or two, some come back with certain activities, and others are truly chronic. I actually felt my better around 27-30 than 20-26. 31+ has been somewhere in-between.
One thing that has definitely changed with age is my heat tolerance. As soon as I hit 31, I could no longer do all day outdoor events. This became apparent when I was training for a century bike ride one summer, and I got so hot, I was feeling tingly and sick. A nurse friend had to pick me up, take me home, and give me an IV, and I wanted to barf for a few hours. And just this summer, I was at a paintball scenario game, and I was so hot that I could barely move; the heat sapped energy, and it didn't matter how much water or Gatorade I drank. When I went back on the field toward the end of the day, I barely had the energy to aim my gun once I hobbled into a position.