The correct answer is option 'A', the 61st Amendment Act.

Explanation:
The voting age in India was initially set at 21 years under the Indian Constitution. However, with the passage of time and changing social dynamics, there was a demand to lower the voting age to 18 years to ensure the participation of young adults in the democratic process.

The amendment act that reduced the voting age from 21 to 18 in India is the 61st Amendment Act. This amendment act was passed by the Indian Parliament in 1988 and received the President's assent on 28th March 1989.

The key details of the 61st Amendment Act are as follows:

1. Objective:
- The primary objective of this amendment act was to lower the voting age from 21 to 18 years.

2. Amendment to Article 326:
- The 61st Amendment Act amended Article 326 of the Indian Constitution, which deals with the "Conduct of Elections to the Lok Sabha and the State Legislative Assemblies."
- The amendment added a clause (4) to Article 326, which states that "Notwithstanding anything in the foregoing provisions of this article, a person who has attained the age of eighteen years shall be entitled to be registered as a voter at any such election."

3. Rationale:
- The decision to lower the voting age was based on the understanding that 18-year-olds are mature enough to exercise their right to vote and make informed decisions.
- It was also seen as a way to encourage the participation of young adults in the democratic process and give them a voice in shaping the future of the country.

4. Impact:
- The 61st Amendment Act had a significant impact on the Indian electoral system.
- It expanded the voting rights of young adults between the ages of 18 and 21, allowing them to participate in the election process and have a say in choosing their representatives.

In conclusion, the 61st Amendment Act is the legislation that reduced the voting age in India from 21 to 18 years. This amendment was aimed at promoting the participation of young adults in the democratic process and giving them a voice in shaping the future of the country.