Be the older cousin who shows the younger ones where the door is, not the one who brags about walking through it.

Getting somewhere first gives you two options, and only one of them is useful to anybody else. You can treat what you learned as a status marker, or you can treat it as directions. The second costs you nothing you actually need and saves the person behind you years of guessing which door was even there.

Think of one thing you figured out that someone younger is still confused about, and tell them how it works. Include the parts that were embarrassing. Skip the version where you sound impressive.