Our expert says:
Not for real. Nobody with expertise would use this term the way he did. There is a concept in psychology of a mental age, meaning the age equivalent of the way one thinks and functions psychologically, and in that sense everyone has a "mental age", and maybe a social age, as the way they behave socially may be different again.
Your friend was probably trying to show off and being pretentious, and merely meaning that the girls is rather immature in how she behaves.
The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical exmanication, diagnosis and formal
advice. Health24 and the expert accept no responsibility or liability for any damage or personal harm you may suffer resulting from making use of this content.