An elderly shop is an old shop.

This reading is an exception, so here's a mnemonic:

You go to an old shop and come across a sheep knee sale (しにせ). When you ask what a sheep knee sale is, the clerk tells you quite matter-of-factly that it's a sale on all the sheep knees. You've never seen this in newer shops, so it must be a pretty old practice to buy and sell sheep knees.