Yeah your argument is correct.
At 18 you can vote, the present-day youth are literate and enlightened and the lowering of the voting age would provide to the unrepresented youth of the country an opportunity to give vent to their feelings and help them become a part of the political process.
It is, therefore, proposed to reduce the voting age from 21 years to 18 years. Hence, the court argument is proved as wrong. 18 have the capability to vote.