Most people believe that their memories get worse as they get older.
This is true only for people who do not use their memories properly: memory is like a muscle - the more it is used, the better it gets. The more it is neglected, the worse it gets.
While in education most people have to use their memories intensively - simply to remember facts and pass exams. When people leave full time education, they tend to cease to use their memory as actively, and so it starts to get flaccid.
How Memory Works
Memory works by making links between information, fitting facts into mental structures and frameworks. The more you are actively remembering, the more facts and frameworks you hold, the more additional facts and ideas will slot easily into long term memory.
Why Memory Doesn't Work!
Another reason for memory getting apparently worse is that outside academia information tends not to be as clearly structured as it is in education. The clear presentation and organisation of a good lesson or training course provides a structure that is almost a mnemonic in its own right. Where information drifts in as isolated facts, it will normally be forgotten simply because it is not actively fitted into a mnemonic.
Again, as people grow up they are trained out of spontaneous, imaginative behaviour: most peoples' jobs depend on them being predictable and reliable far more than on them being imaginative. An important feature of memory, though, is the imagination that allows you to construct the strong mnemonic links between things to be remembered and the cues for their recall. Of course be reliable, but keep your imagination fresh at the same time!
So memory in most people does get worse with age, but only because it is allowed to. By continuing your education throughout your life, by cultivating your mind and keeping it open to new experience, by actively fitting facts into clear and flexible frameworks, and by keeping your imagination working, your memory can get better and better as you get older.
Doing this not only gives you a better memory: think how many times you have heard this message in connection with other self-improvement methods! An important thing to realise is that different people learn in different ways. The way in which people learn is often a factor determining the subjects they choose to study, instructors they relate to, and careers chosen in life.