It can be complicated, depending on the quality of the source of each date. Usually needs additional research, or enter both dates.
But in this case the document you’ve attached can only (IMHO) have an error in the date of 1951 at the bottom.
It’s surely impossible to know a birth date 2 years in the future! Assuming you have checked that the date of birth (1953) is correct.
So I would record the date of naturalisation as 1953, but of course with a note explaining the reason for that decision. I tend to take care to use words like “assumption” snd “believe” to emphasise that the action ignoring the recorded date is “reasonable” rather than “factual”.