The oldest person alive was once the youngest person in a room.

Every very old person was once the youngest in the room, being told they had plenty of time, and the transition between those two states happened without a single day feeling like the turning point. Age arrives continuously while the categories it puts you in change abruptly.

This works in both directions. If you are the youngest somewhere, that will not last, so use the position while it is yours. If you are the oldest, remember what it was like to be the one presumed to know nothing, and make room for whoever is in that seat now.