Assuming you spend lots of your day at a desk, in just a few related postures, you'd do well to think far more about
mobility than you currently seem to be.
Running and lifting are both great, but running is pretty repetitive and uniform and gets moreso the better you get at it. And lifting that most people explore is usually focused on increasing power (and/or bulk) in a just few major muscle groups.
And all that is really great, but if you're feeling achy and stiff, those aren't aimed very well at the problem.
Think about stuff that's more dynamic and varied: dance, pilates, yoga, gymnastics, martial arts, rock climbing, etc. If you take any of those seriously, they all have deep progressions with high skill ceilings that can hold your interest and create the same kind of feedback loop of pride and accomplishment that you probably find in running and lifting already.
If you're near a big city, you might also be able to go a little further into the massage and movement world with practices like rolfing, alexander technique, or feldonkrais. These are more passive and induce less progressive/permanent change, but can provide a radical change to the way you feel.
Meditation can help, too.