Let the older person finish choosing before deciding the choice is taking too long.

Impatience with a slow decision is usually impatience with your own schedule. An older person weighing something at a counter may be checking a price against a fixed income, or simply enjoying a decision that is entirely theirs to make. Stepping in to speed it up takes the choosing away, which is often one of the few things left fully in their hands.

When you are waiting, let the pause run. Offer information if it is asked for and keep your body still rather than shifting toward the door. If you are genuinely pressed for time, say so plainly instead of hurrying them silently, which everyone can feel.