“House - (3) four year terms
Senate - (2) six year terms
THEN DONE”
Yes, so long as the “in the aggregate,” no one can serve more than twelve years combining their House and Senate “service.” So they will not be able to serve 12 years on one body and another 12 in the other.
How about this: A member of Congress cannot serve more than 12 years. By specifying Congress, both the House and the Senate are included.
Also need something to prevent multiple 12 year terms with a term off in the middle. 12 years and you’re done for life.