“You’ll get it when you’re older” is annoying mostly because it keeps turning out to be true.

Some understanding needs experience as an ingredient and cannot be handed over in a sentence. That is what makes the phrase infuriating: dismissive in delivery, frequently correct in content, which is the worst possible combination. Adults use it lazily, sometimes to dodge explaining themselves, and that part is fair to resent. The annoying bit is how often the thing they could not explain turns up later exactly as described.

When you hear it, file the claim instead of rejecting it. Ask what specifically changed for them. Then leave the file alone and see whether it opens on its own.