Some degree of memory problems, as well as a modest decline in other thinking skills, is a fairly common part of aging.
There's a difference, however, between normal changes in memory and memory loss associated with Alzheimer's disease and related disorders. And some memory problems are the result of treatable conditions.
1. Article/Fact Sheet:
Memory loss: Just a sign of aging, or something more?
This article discusses what different types of memory loss can mean.