congratulations, beautiful pup and welcome to the club. yeah, shark attacks are definitely something to learn to deal with. but then again, puppy age has so many heartwarming memories to create, enjoy it, they grow up way too fast.
These stairs seem way to high for your pup to climb at this age, your worry related to the joints is valid in my view. It is an eternal dilemma: you want them to learn things but then again not at the cost of their health. If your have smaller interval stairs in your household i would let him practice there and try avoid these very high looking ones for a while.