Answer:
The current rules for voting is that you must be a 18 years old, or older, an American Citizen, and you MUST be registered to vote. It has changed because back then, only White men, with property could vote, then it was Men with Property could vote, then ALL MEN could vote, then women got there right, and much more. It has changed for a long time, and lastly back then, you had to be 21 to vote, which was decreased.
Hope this helps! Stay Safe!