In the vaguest sense, as long as you have ilvl required to do a dungeon, you are qualified to do the dungeon. Generally people won’t care as long as you make some effort to keep gear relatively up to date.

If you are nervous about it, just do it with NPCs and re-equip with dungeon drops. All the drops for you, and no complaining players! Win win.

Final raid or tomestone gear from each expac will generally last until the 3rd dungeon (so 65/75/85), where you can replace with drops from said dungeon.