Conversation so far:
when did the voting age get lowered to 18
On July 5, 1971, President Richard Nixon formally certified the 26th Amendment of the Constitution, which granted 18 year olds the right to vote.
who certified the adoption of the 26th amendment
The Administrator of General Services, Robert Kunzig, certified the adoption of the 26th amendment

Question: Who were the witnesses?
Self-contained rewrite: Who were witnesses to the passage of the 26th amendment besides Robert Kunzig?