I'm not sure if this is the right section of the forum but what causes memory problems and at what age is it normal for problems to occur?

This question would need a whole book to be answered. 
In short: there are many types of brain injuries associated to memory problems such as : stroke,brain turmors, head trauma,cerebrovascular disorders, cerebral infections and others. Also a lot of others patologies such as Alzheimer disease or dementia ( just to name two of many ) can cause memory loss. 

In order to have strong memory problems, usually, there are three main areas that mainly needs to be damaged ( note that the type of damage and the area where it happens can determine many different deficit) : 

1. Mid-Dorsal Nucleus of the Thalamus

2. Mamillary bodies

3. Hippocampus 

All of the above are neuropsychological diseases caused by brain injuries that do not occur normally. 
Memory loss can occur also with age ( the age at which they occur  mostly depends on the individual lifestyle), and its usually caused by the deterioration of neural synapsis in the brain. Note that recent studies show that intellectual activities, physical activities and general learning can drastically reduce normal memory loss. 

Edited April 6, 20196 yr by Elendirs
grammar