Aquarium,congrats on getting it taken care of sucessfully!
The sand can wear out, however it takes a long time. Actually slightly dirty, or aged sand, filters better than new, the pathways between the individual grains gets smaller either due to the dirt it's already collected or because the edges get erroded so the sand can 'snuggle up' a little closer to is fellow grains - this allows smaller particles to be trapped. Well cared for sand should last 10 + yrs.