Is this statement grammatically correct?
My parents didn't buy me a laptop until my 20.
I mean by 20 years, or is the following sentence better?
My parents had not bought me a laptop before I became 20 years old.
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Sign up to join this communityIs this statement grammatically correct?
My parents didn't buy me a laptop until my 20.
I mean by 20 years, or is the following sentence better?
My parents had not bought me a laptop before I became 20 years old.
Is this statement grammatically correct?
My parents didn't buy me a laptop until my 20.
it isn't. This would require "20" to be some noun possessed by you. What you're trying to say is "...until I was 20" (i.e. years old) or "...until my 20th birthday" (if it was on that specific day) or "...until my 20th year" (although that sounds fairly archaic).
[I]s the following sentence better?
My parents had not bought me a laptop before I became 20 years old.
no. Why did you change the tense of the first half when it was the second half that had the problems? You'd only use the pluperfect like this if you had already mentioned a different thing in the past and this was before it. It's more natural to use the simple past, like you did before: "My parents didn't buy me a laptop until I turned 20" or "...until my 20th birthday" &c.
In the first example cited by the OP, the following is acceptable:
…didn't buy me a laptop until I was in my twenties
Someone in their twenties can be any age between 20 and 29. In order to narrow the age range down, the OP can say something like this
If you want to express that your parents bought you a computer when you were 20 and emphasize that they did not buy you one before then, we would most likely say:
My parents didn't buy me a laptop until I was 20.
The sentence that you ask about is very likely grammatically correct though I strongly suspect that you actually want to know if it's acceptable. It is not acceptable.
Without getting unduly technical, we can informally demonstrate that your first sentence is grammatical, in the way that most modern linguists would use that term, by substituting some other words from the same class as each lexeme:
Her boss didn't offer her a raise until her evaluation.
Most native or highly proficient speakers of English would easily judge that utterance as grammatical and acceptable. Since My parents didn't buy me a laptop until my 20 is structurally equivalent, it is also "grammatical", whether or not it makes sense.
Your second sentence is probably not better, because I doubt that it expresses what you want to express.
It is, however, just as good if we evaluate on the basis of grammaticality, and it is, in fact, better if we evaluate on acceptability provided it occurs in an appropriate context, because that is something that would be acceptably uttered in standard English, in an appropriate context.