Ye. The noun "childhood" may be used as an adjective modifying another noun " days."
It depends on the context, childhood itself portrays the days a person spend in childhood, so there is no need to explicitly specify childhood days. But in common usage childhood days is used.
Yes, the sentence "I have been in love with him since childhood" is grammatically correct. It uses the present perfect tense to express an action that started in the past and continues into the present.
Neither one makes sense, but "How many days are you?" is grammatically correct.
"Not like that" can be grammatically correct, depending on the context.
Yes! That is grammatically correct!
Yes, 'for free', is grammatically correct.
This is not grammatically correct. The correct form is 'you do not know', or the abbreviated 'you don't know'.
"That was wrong" is a grammatically correct sentence.
'What a drunkard you are' is a grammatically correct English sentence.
Yes, Almighty God is grammatically correct.
Yes, it is grammatically correct.
Sure. It would also be grammatically correct to write He spoggled his nubbix on the goober. Grammatically correct and meaningful are not the same.
The phrase "Is you don't miss me do you" is not grammatically correct. It should be rephrased to something like "Don't you miss me?" to be correct.