Why should an old red be decanted gently when a young red gets splashed?

Answer: Sediment, not workout

Older wine needs hours — No. Old bottles are often more fragile, not more eager for oxygen. Some aged reds are decanted mainly to remove sediment and may lose their best window after too much air. A young, tannic red can use oxygen as a workout; an old red may need a careful transfer.

Sediment, not workout ✓ — Correct. In an older red, the decanter is often a separator, not a gym. Pigments and tannins can form sediment over years, so a slow pour keeps grit in the bottle. The counterintuitive part is that the fanciest old wine may need less breathing than the cheaper, younger, tougher one.

Sediment needs oxygen — Not quite. Sediment is solid material from aging pigments and tannins; oxygen does not dissolve it into better flavor. The point of a gentle decant is to leave that grit behind in the bottle. A young red may need air, but an old red often needs separation.