“Just wait until you’re older” is annoying and partly true. Some of it you’ll only get by living it.

It gets used to dismiss you, which is unfair and often lazy. The true part is narrow but real: some understanding only arrives through having been through things, and no explanation substitutes for that. You can be right now and still learn more about it in ten years, which is not the same as being wrong today.

Separate the two when you hear it. If somebody is using it to avoid answering, ask them for the actual reason. If they are describing something they only learned by living it, ask what changed their mind, because that is a real answer.