Activities that are hard on your body, and 100% physical, can be really unforgiving when it comes to the aging process.
With rock climbing you can kind of shift your focus.. maybe do more trad climbing instead of sport or bouldering. Focus on different types of climbs, maybe more technical slabby climbs where you're on your feet more. You can still feel like you're genuinely participating in the activity you love, even if you can't do exactly the same things you did before to the same extent.