Which one is more correct ? Over or more than .in this sentence1:To enter the casino u need to be .............18 years old.
The correct one is 'over'.
'More than' is a comparative structure and if you compare, you need to compare two or more things. In the sentence you provided, there is not any comparison so 'more than' makes no sense at all.
'More than' -> Comparative structure. For example: I am taller THAN my sister. After 'THAN' we always need a name (Person, object, element ...). E.g: Diamonds are more expensive than silver.
Just remember, just use 'more than' when you are comparing two or more elements.
Hope this helps.