In the u.k the word "retarded" would be seen as quite offensive. We use terms such as "mental impairment/having a learning difficulty/cognitive disability". However, through different research, in response to your question, I have heard the term "mentally challenged" and "mentally retarded".
mentally chalenged
Special needs is the politically correct term for someone who is mentally, emotionally, or physically challenged. In the past, hurtful people would say retarded.
Disabled, or for a person with a mental disability, you can use the term "mentally challenged."
Mentally retarded is not a medical term. A brain hemorrhage may cause brain damage that could affect one or many functions of the brain.
According to the World Health Organization, the proper term is "mental retardation". However, this is expected to change to in the next revision of the ICD codes to something like "intellectual disability" or "intellectual development disorder" (this is what the DSM already uses).
A mitigating circumstance. An example would be the defendant is mentally retarded or mentally ill.
How about "the chronologically challenged".
That would be "developmentally challenged".
No but it can cause long term physcological and short term problems like feeling depressed and insecure
You were either born with it (due to genetics), or you have suffered some kind of brain injury as a result of trauma or lack of Oxygen. Even people with dementia and Traumatic Brain Injury later in life can resemble someone who's "retarded". Personally, I prefer the term "mentally disabled".
George W. Bush, two-term president of the United States, graduate of Yale University and the Harvard Business School, has occasional problems with syntax. I found his geopolitical worldview to be simplistic, but he is not mentally challenged.
physically challenged man
An IQ of 56 is considered very, very low. Generally, anyone below 70 is considered to be intellectually challenged (or retarded, but that is an ugly term).