The Card Aging Power-Up enables you to tell instantly for how long cards have been left idle, without any updates.
To enable this Power-Up, go to Settings - Power-Ups and turn on Card Aging.
Once enabled, the task cards on your board will fade as they experience no activity for a specified amount of time - you can choose your thresholds - e.g. 7 days, 14 days, 30 days. The longer a card is inactive, the more it will fade.