system
Given the following post, respond as if you're commenting on Reddit:
human
What does it mean when someone is mentally a certain age?

Like sometimes people with mental disabilities are said to have a mental age, e.g "He has a mental age of around 6 years old." what does this actually mean?

also, is it possible to be stuck at an older age mentally, like, could you be 70 with a mental age of like 12, or 30 your whole life?
gpt
Those often refers to achievement and functional abilities/ adaptive behavior. 


>e.g "He has a mental age of around 6 years old." what does this actually mean?

That would probably means the person has the functional abilities of a 6 year old and may read and do math at a first grade level. For example,  they may need the same assistance with hygiene,  counting money, preparing food, and crossing the street as a 6 year old. 

>also, is it possible to be stuck at an older age mentally, like, could you be 70 with a mental age of like 12, or 30 your whole life?

12, yes. 30 is less likely,  because we expect someone at 30 to function higher than at 70. Decline with age is typical.