The correct answer is option 3, which is 25 years. In order to contest a Parliamentary election, the candidate`s age should be at least 25 years. Option 1, which is 18 years, is incorrect as it is the minimum age required to vote in an election, not to contest it. Option 2, 21 years, is also incorrect as it is the minimum age required to contest a State Assembly or Legislative Council election, not a Parliamentary election. Option 4, 26 years, is also incorrect as it is not mentioned in the question and is above the age limit required to contest a Parliamentary election. Therefore, the correct age to contest a Parliamentary election is 25 years.