i disagree. by age 18 they should have to declare. that’s 3 more years of mental instability not declaring which country they want to truly be loyal to. 18 is when you leaglly vote - I don’t what mentally undecleared dual citizens voting - or at least least amount possible since we have some much vote cheating going one already.
Look at some clear history our pre and founding era had grade schoolers or teens who understood so much more about loyalty to country and knowing who the enemies of USA freedom ideals were and how to keep them in check. They also were well learned and studied on foreign countries too. wall builders.com David Barton has great info and documents of founding era writings - it’s amazing the people we had and thought and prayer that went into creating our USA.
My thought is that most 18 year old’s are immature this is a mature decision. I want the person to take the time to think about what they are doing. I would say you are right about them not being able to vote. until they declare there should be no participations in elections, serving in the military or sitting on juries. I would say there rights with in the law should be the same as a foreign visitor. they just have the ability to fill out the paper work during the that time for full citizenship and renouncing the foreign citizenship.