Question

at what age can you register to vote?
21 years old
18 years old
25 years old

Explanation:

In most democratic systems (including the US, where this standard is widely recognized), the legal voting age, and thus the age to register to vote, is set at 18. This was established via constitutional amendments (like the 26th Amendment in the US) to lower the voting age from 21.

Answer:

18 years old