12/18/1866
https://www.presidency.ucsb.edu...
"No one who is not 21 years of age at the time of registration can take the oath."
"An unnaturalized person can not take this oath, but an alien who has been naturalized can take it."
"The oath prescribed in the supplemental act defines all the qualifications required, and every person who can take that oath is entitled to have his name entered upon the list of voters."
"A person forced into the rebel service by conscription or under a paramount authority which he could not safely disobey, and who would not have entered such service if left to the free exercise of his..."