Option 1: The 42nd Constitutional Amendment Bill did not lower the voting age from 21 to 18 years.

Option 2: The 44th Constitutional Amendment Bill also did not lower the voting age from 21 to 18 years.

Option 3: The Gist Constitutional Amendment Bill did not directly address the voting age. Therefore, it is not the correct answer.

Option 4: The 73rd Constitutional Amendment Bill also did not lower the voting age from 21 to 18 years.

Therefore, the correct answer is not provided among the given options. Alert - The correct answer should be the 61st Constitutional Amendment Bill. This amendment, passed in 1988, lowered the voting age from 21 to 18 years, enabling more young citizens to participate in the democratic process.